Enzymes Glycolysis PDF

**[Enzymes]** ========================= 1\] Glycolysis ============== +-----------------------------------+-----------------------------------+ | **1\]** | **[Hexokinase]** | +===================================+===================================+ | **Reaction**...

**[Enzymes]** ========================= 1\] Glycolysis ============== +-----------------------------------+-----------------------------------+ | **1\]** | **[Hexokinase]** | +===================================+===================================+ | **Reaction** | **Glucose → Glucose-6-phosphate** | +-----------------------------------+-----------------------------------+ | **Effects** | | +-----------------------------------+-----------------------------------+ | **Regulators** | Inhibited by its own product - | | | Glucose-6-phosphate | +-----------------------------------+-----------------------------------+ | **Other info** | Glycolysis step 1 | | | | | | Very strong affinity (low Km) for | | | glucose, Vmax low (total number) | +-----------------------------------+-----------------------------------+ +-----------------------------------+-----------------------------------+ | **2\]** | **[Glucokinase]** | +===================================+===================================+ | **Reaction** | **Glucose → Glucose-6-phosphate** | +-----------------------------------+-----------------------------------+ | **Effects** | | +-----------------------------------+-----------------------------------+ | **Regulators** | Activated after high carb meals | | | | | | Not inhibited by G6P. | | | | | | Hormone effect:Insulin | | | upregulates, Glucagon | | | downregulates | +-----------------------------------+-----------------------------------+ | **Other info** | Glycolysis step 1 | | | | | | Weak affinity (high Km) for | | | glucose, Vmax high (total number) | +-----------------------------------+-----------------------------------+ **3\]** **[Phosphoglucose isomerase]** -------------- ------------------------------------------------ **Reaction** **Glucose-6-phosphate → Fructose-6-phosphate** **Effects** Glycolysis step 2 +-----------------------------------+-----------------------------------+ | **4\]** | **[Phosphofructokinase 1 | | | (PFK-1).]** | +===================================+===================================+ | **Reaction** | **fructose-6-phosphate → fructose | | | 1,6-bis-phosphate** | +-----------------------------------+-----------------------------------+ | **Effects** | Requires ATP | +-----------------------------------+-----------------------------------+ | **Regulators** | Activated by: AMP, fructose | | | **2**,6-bis-phosphate | | | | | | Inhibited by: ATP, Citrate | | | | | | Hormone effect:Insulin | | | upregulates, Glucagon | | | downregulates | +-----------------------------------+-----------------------------------+ | **Other info** | Glycolysis step 3 | +-----------------------------------+-----------------------------------+ +-----------------------------------+-----------------------------------+ | **5\]** | **[Glyceraldehyde 3-phosphate | | | dehydrogenase]** | +===================================+===================================+ | **Reaction** | **glyceraldehyde 3-phosphate → | | | 1,3-bisphosphoglycerate (1,3 | | | BPG)** | +-----------------------------------+-----------------------------------+ | **Effects** | Requires inorganic phosphate | | | | | | Converts NAD to NADH + H+ | +-----------------------------------+-----------------------------------+ | **Regulators** | Inhibited by the poison arsenic. | +-----------------------------------+-----------------------------------+ | **Other info** | Glycolysis step 6 | +-----------------------------------+-----------------------------------+ **6\]** **[Phosphoglycerate kinase.]** ---------------- ---------------------------------------------------------------------- **Reaction** **1,3-bisphosphoglycerate (1,3 BPG) → 3-phosphoglycerate.** **Effects** Phosphate released - ATP produced by substrate level phosphorylation **Regulators** **Other info** Glycolysis step 7 **7\]** **[2,3-BPG mutase]** ---------------- --------------------------------------------------------------- **Reaction** **1,3-bisphosphoglycerate (1,3 BPG) → 2,3-phosphoglycerate.** **Effects** Stabilises Deoxyhemoglobin - releases O2 **Regulators** **Other info** Alternate step to glycolysis step 7 **7\]** **[Phosphoglycerate mutase]** ---------------- --------------------------------------------------- **Reaction** **3-phosphoglycerate to 2-phosphoglycerate** **Effects** Low E phosphate bond → High energy phosphate bond **Regulators** **Other info** Glycolysis step 8 +-----------------------------------+-----------------------------------+ | **7\]** | **[Pyruvate kinase]** | +===================================+===================================+ | **Reaction** | **Phosphoenolpyruvate (PEP) → | | | pyruvate** | +-----------------------------------+-----------------------------------+ | **Effects** | Phosphate released - ATP produced | | | by substrate level | | | phosphorylation | +-----------------------------------+-----------------------------------+ | **Regulators** | Activation: fructose | | | 1,6-bisphosphate | | | | | | Hormone effect:Insulin | | | upregulates, Glucagon (fasting) | | | downregulates | +-----------------------------------+-----------------------------------+ | **Other info** | Glycolysis step 9 | +-----------------------------------+-----------------------------------+ NOTE: **Insulin:** Activates Protein Phosphatases → leading to enzyme dephosphorylation **Glucagon:** Activates Protein Kinase → leading to enzyme phosphorylation 2\] Fate of NADH ================ **7\]** **[Lactate dehydrogenase]** ---------------- ----------------------------------------- **Reaction** **Pyruvate → lactate** **Effect** NADH → NAD **Regulators** **Other info** Regenerate NAD **[3\] Glycolysis linked to TCA]** ============================================== +-----------------------------------+-----------------------------------+ | **8\]** | **[Pyruvate dehydrogenase | | | (PDH)]** | +===================================+===================================+ | **Reaction** | **Pyruvate → Acetyl CoA** | +-----------------------------------+-----------------------------------+ | **Effect** | Produces CO2, NADH + H+ | +-----------------------------------+-----------------------------------+ | **Regulators** | Coenzymes: Thiamine | | | pyrophosphate, lipoic acid and | | | CoA, FAD and NAD+. | | | | | | Activation: Ca2+ → activate → | | | pyruvate dehydrogenase kinase → | | | activates PDH | | | | | | Inhibition: Acetyl CoA and NADH | | | | | | Phosphorylated - inactive - by | | | PDH kinase - (activated by ATP, | | | Acetyl CoA, NADH, | | | | | | Unphosphorylated - active - by | | | Phosphoprotein phosphokinase | | | (activated by Ca2+) | | | | | | Inhibition: Product inhibition: | | | Products: Acetyl CoA and NADH | | | | | | Covalent inhibition: Pyruvate | | | dehydrogenase kinase (PDH kinase) | +-----------------------------------+-----------------------------------+ | **Other info** | From glycolysis to TCA | | | | | | In mitochondrial matrix | +-----------------------------------+-----------------------------------+ **[4\] TCA]** +-----------------------------------+-----------------------------------+ | **9\]** | **[Citrate | | | synthase]** | +===================================+===================================+ | **Reaction** | **acetyl CoA + oxaloacetate → | | | citrate** | +-----------------------------------+-----------------------------------+ | **Effect** | Produces CoA, | | | | | | Citrate inhibits the | | | rate-limiting glycolytic enzyme | | | phosphofructokinase | +-----------------------------------+-----------------------------------+ | **Regulators** | Inhibition: Citrate (product), | | | NADH, Succinyl CoA, Substrate | | | availability | +-----------------------------------+-----------------------------------+ | **Other info** | TCA step 1 | | | | | | Also - source of acetyl CoA for | | | fatty acid synthesis | +-----------------------------------+-----------------------------------+ **10\]** **[Aconitase ]** ---------------- --------------------------------------------------- **Reaction** **citrate → isocitrate** **Effect** isomerization **Regulators** Inhibition: fluoroacetyl CoA (from fluoroacetate) **Other info** TCA step 2 +-----------------------------------+-----------------------------------+ | **11\]** | **[Isocitrate | | | dehydrogenase]** | +===================================+===================================+ | **Reaction** | **Isocitrate → a-ketoglutarate.** | +-----------------------------------+-----------------------------------+ | **Effect** | Produces NADH + H+, CO2 | +-----------------------------------+-----------------------------------+ | **Regulators** | Activation: Ca2+, ADP | | | | | | Inhibition: NADH, ATP | +-----------------------------------+-----------------------------------+ | **Other info** | TCA step 3 | +-----------------------------------+-----------------------------------+ +-----------------------------------+-----------------------------------+ | **12\]** | **[A-ketoglutarate | | | dehydrogenase]** | +===================================+===================================+ | **Reaction** | **A-ketoglutarate → Succinyl | | | CoA** | +-----------------------------------+-----------------------------------+ | **Effect** | Requires CoA | | | | | | Produces NADH + H+, CO2 | +-----------------------------------+-----------------------------------+ | **Regulators** | Coenzymes: thiamine | | | pyrophosphate, CoA, lipoic acid, | | | NAD+ and FAD. | | | | | | Activation: Ca2+, | | | | | | Inhibition: NADH, GTP, succinyl | | | CoA, | +-----------------------------------+-----------------------------------+ | **Other info** | TCA step 4 | | | | | | Alpha-ketoglutarate is also | | | produced in a different reaction | | | from the amino acid glutamate. | +-----------------------------------+-----------------------------------+ +-----------------------------------+-----------------------------------+ | **13\]** | **[Succinate | | | thiokinase.]** | +===================================+===================================+ | **Reaction** | **Succinyl CoA → Succinate** | +-----------------------------------+-----------------------------------+ | **Effect** | Produces GTP, CoA | | | | | | Substrate level phosphorylation | | | of GDP to form GTP. | +-----------------------------------+-----------------------------------+ | **Regulators** | | +-----------------------------------+-----------------------------------+ | **Other info** | TCA step 5 | +-----------------------------------+-----------------------------------+ +-----------------------------------+-----------------------------------+ | **14\]** | **[Succinate | | | thiokinase]** | +===================================+===================================+ | **Reaction** | **Succinate → Fumarate** | +-----------------------------------+-----------------------------------+ | **Effect** | Produces FADH2 | +-----------------------------------+-----------------------------------+ | **Regulators** | | +-----------------------------------+-----------------------------------+ | **Other info** | TCA step 6 | | | | | | Fumarate is produced by other | | | metabolic reactions | | | | | | - - - | +-----------------------------------+-----------------------------------+ **15\]** **[Fumarase ]** ---------------- ----------------------------- **Reaction** **Fumarate → Malate** **Effect** Requires H2O **Regulators** **Other info** TCA step 7 **16\]** **[Malate dehydrogenase]** ---------------- ---------------------------------------- **Reaction** **Malate → Oxaloacetate** **Effect** Produces NADH + H+ **Regulators** Inhibition: NADH **Other info** TCA step 8 **TCA intermediates as precursors** +-----------------------------------+-----------------------------------+ | **17\]** | **[Pyruvate | | | carboxylase]** | +===================================+===================================+ | **Reaction** | **Pyruvate → Oxaloacetate** | +-----------------------------------+-----------------------------------+ | **Effect** | Produces ATP | +-----------------------------------+-----------------------------------+ | **Regulators** | Coenzyme: Biotin | | | | | | Activation: Acetyl CoA | +-----------------------------------+-----------------------------------+ | **Other info** | Entry to TCA when Acetyl CoA is | | | in xs | +-----------------------------------+-----------------------------------+ 5\] ETC and oxidative phosphorylation ===================================== **18\]** **Complex I: [NADH dehydrogenase]** ---------------- ------------------------------------------------------------------ **Reaction** **Electron route: NADH → FeS → CoQ** **Effect** 4 H+ pumped into intermembrane space **Regulators** Inhibitors: Rotenone (an insecticide), Amobarbital (barbiturate) **19\]** **Complex II: [Succinate dehydrogenase]** ---------------- ------------------------------------------------------- **Reaction** **Electron route: FADH2 → CoQ** **Effect** No H+pumped **Other info** Also enz in TCA cycle **20\]** **[Coenzyme Q]** -------------- ----------------------------------------------------------------------------------- **Reaction** **Reduced Quinol form → Semiquinone form → Oxidised quinol form (of CoQ itself)** **Effect** Accepts 2 H+ and 2 e- **21\]** **Complex III: [ Cytochrome bc1 ]** ---------------- ------------------------------------------------- **Reaction** **Electron route: CoQ → FeS → Cyt c** **Effect** Transports 2 H+ intermembrane space **Regulators** Inhibitors: Antimycin A (antibiotic) **22\]** **Complex IV: [ Cytochrome c oxidase ]** ---------------- --------------------------------------------------------------------- **Reaction** **Electron route: Cyt c → O2** **Effect** Transports 4 H+ into intermembrane space, Gives 4e- to O2 **Regulators** Inhibitors: Cyanide , azide, CO **Other info** Higher affinity (lower Km) for oxygen than myoglobin or haemoglobin **23\]** **[ATP synthase]** ---------------- --------------------------------------------------------------------------- **Reaction** **ADP + P → ATP** **Effect** As the H+ ins go through it to go back to the membrane - ATP is generated **Regulators** Inhibitors: Oligomycin (antibiotic) **24\]** **[ATP-ADP translocase]** ---------------- ---------------------------------------------------------------------------- **Effect** Transports Substrates ADP and P into matrix, and product ATP out of matrix **Regulators** Inhibitors: Atractyloside **Note: Dinitrophenol: Inhibitor of ETC - uncouples ATP from ETC - no specific site** 6\] Glycogen metabolism ======================= **Glycolysis** +-----------------------------------+-----------------------------------+ | **1\]** | **[Phosphoglucomutase]{.underline | | | }** | +===================================+===================================+ | **Reaction** | **Glucose-6-phosphate → | | | Glucose-1-phosphate** | +-----------------------------------+-----------------------------------+ | **Effect** | Isomerisation | +-----------------------------------+-----------------------------------+ | **Regulators** | | +-----------------------------------+-----------------------------------+ | **Other info** | Facilitates entry into glycolysis | | | and gluconeogenesis - | | | | | | \- this reaction reversible - | | | also used in glycogenolysis | +-----------------------------------+-----------------------------------+ +-----------------------------------+-----------------------------------+ | **2\]** | **[Glycogenin]** | +===================================+===================================+ | **Reaction** | **Initiates chain of | | | UDP-glucose** | +-----------------------------------+-----------------------------------+ | **Effect** | Serves as an anchor for the first | | | few (4-8) glucose residues from | | | UDP-glucose. | | | | | | Glucose is added to the chain - | | | UDP is released | +-----------------------------------+-----------------------------------+ | **Regulators** | | +-----------------------------------+-----------------------------------+ | **Other info** | Initiates glycolysis chain | | | formation | +-----------------------------------+-----------------------------------+ +-----------------------------------+-----------------------------------+ | **3\]** | **[Glycogen | | | synthase]** | +===================================+===================================+ | **Reaction** | **Continues addition of Glucose | | | to the chain (1-4 glycosidic | | | bonds)** | +-----------------------------------+-----------------------------------+ | **Effect** | Glucose is added to the chain - | | | UDP is released | +-----------------------------------+-----------------------------------+ | **Regulators** | Activation: Glucose-6-phosphate | | | (both liver and muscle) | | | | | | Liver:Hormonal regulation: | | | Insulin upregulates, Glucagon | | | downregulates | | | | | | Muscle: Inhibition: Glycogen | | | (stronger than liver) | | | | | | - | | | | | | Inhibition: **Protein kinase** - | | | (inactivates )phosphorylates | +-----------------------------------+-----------------------------------+ | **Other info** | Elongates chain in glycolysis | | | chain formation | +-----------------------------------+-----------------------------------+ **4\]** **[Branching enzyme - 4,6-transferase]** ---------------- ------------------------------------------------------------------------------------------- **Reaction** **Joins chains of glucose together forming branches (1-6 glycosidic bond)** **Effect** Joins chains around 11 residuals long - glycogenin of chain which is attached is released **Other info** Final step of Glycolysis - non reducing ends joined together (glycogenin ends) **Glycogenolysis - breakdown of glycogen** +-----------------------------------+-----------------------------------+ | **5\]** | **[Glycogen | | | phosphorylase]** | +===================================+===================================+ | **Reaction** | **Glycogen chain + phosphate → | | | glucose-1-phosphate + remaining | | | chain** | +-----------------------------------+-----------------------------------+ | **Effect** | Removes a glucose from the | | | glycogen chain - needs phosphate | +-----------------------------------+-----------------------------------+ | **Regulators** | Coenzyme: Pyridoxal phosphate | | | | | | Liver: Inhibitors: | | | Glucose(allosteric inhibitor), | | | ATP, Glucose-6-phosphate | | | | | | Hormone regulation: Glucagon | | | upregulates, Epinephrine | | | upregulates | | | | | | - | | | | | | Muscle: Inhibition: ATP, | | | Glucose-6-phosphate | | | | | | Muscle: Activation: Ca2+(neural), | | | AMP, epinephrine | +-----------------------------------+-----------------------------------+ | **Other info** | Glycogenolysis - breakdown of | | | glycogen | | | | | | The branches are removed by the | | | debranching enzyme | | | | | | Pyridoxal phosphate is the active | | | form of vitamin B6. | +-----------------------------------+-----------------------------------+ Note: Glucose-1-phosphate → Glucose-6-phosphate **6\]** **[Glucose 6 phosphatase]** ---------------- ------------------------------------------------------------------- **Reaction** **Glucose-6-P → Glucose (liver)** **Effect** Gives off free glucose and phosphate **Regulators** **Other info** End of glycolysis - free glucose released into blood (from liver) Note: Glycogen phosphorylase - active when phosphorylated Glycogen synthase - active when unphosphorylated 7\] Gluconeogenesis =================== 1. **1\]** **[Glycerol kinase]** ---------------- ---------------------------------------- **Reaction** **Glycerol → Glycerol-3-phosphate** **Effect** **Regulators** **Other info** Entry of Gluconeogenesis from glycerol +-----------------------------------+-----------------------------------+ | **2\]** | **[Glycerol 3 phosphate | | | dehydrogenase]** | +===================================+===================================+ | **Reaction** | **Glycerol-3-phosphate → | | | Dihydroxyacetone phosphate** | +-----------------------------------+-----------------------------------+ | **Effect** | **dihydroxyacetone phosphate** | | | (intermediate of glycolysis) | | | | | | Can be converted to G3P | +-----------------------------------+-----------------------------------+ | **Regulators** | | +-----------------------------------+-----------------------------------+ | **Other info** | Entry of Gluconeogenesis from | | | glycerol | +-----------------------------------+-----------------------------------+ 2. **\]** **[Lactate dehydrogenase]** ---------------- ----------------------------------------------------------------- **Reaction** **lactate → pyruvate** **Effect** Produces NADH **Regulators** **Other info** Stand alone formation of pyruvate to be used in gluconeogenesis **\]** **[Alanine aminotransferase]** ---------------- ----------------------------------------------------------------- **Reaction** **Alanine → pyruvate** **Other info** Stand alone formation of pyruvate to be used in gluconeogenesis Pyruvate to Phosphoenolpyruvate - - - - NOTE: fasting we need gluconeogenesis - we need Pyruvate → Phosphoenolpyruvate **REACTION 1: Pyruvate to Phosphoenolpyruvate** +-----------------------------------+-----------------------------------+ | **\]** | **[Pyruvate | | | carboxylase]** | +===================================+===================================+ | **Reaction** | **Pyruvate → Oxaloacetic acid** | +-----------------------------------+-----------------------------------+ | **Effect** | | +-----------------------------------+-----------------------------------+ | **Regulators** | Coenzyme: Biotin | | | | | | Activation: High acetyl CoA (from | | | fatty acid degradation) | | | | | | Inhibition: Low acetyl CoA | +-----------------------------------+-----------------------------------+ | **Other info** | (This pyruvate can be derived | | | from lactate and alanine - above | | | reactions) | +-----------------------------------+-----------------------------------+ +-----------------------------------+-----------------------------------+ | **\]** | **[Phosphoenolpyruvate | | | carboxykinase | | | (PEPCK)]** | +===================================+===================================+ | **Reaction** | **Oxaloacetic acid → | | | Phosphoenolpyruvate** | +-----------------------------------+-----------------------------------+ | **Effect** | GTP used, CO2 produced | +-----------------------------------+-----------------------------------+ | **Regulators** | Hormone regulation: Upregulation: | | | Glucagon (fasting) and | | | Epinephrine (stress) | | | | | | - | +-----------------------------------+-----------------------------------+ | **Other info** | PEP → intermediate for | | | gluconeogenesis | +-----------------------------------+-----------------------------------+ **REACTION 2: phosphofructokinase fructose 1,6-bisphosphate to fructose 6-phosphate** +-----------------------------------+-----------------------------------+ | **\]** | **[Fructose | | | 1,6-bisphosphatase]** | +===================================+===================================+ | **Reaction** | **Fructose 1,6-bisphosphate → | | | Fructose 6-phosphate + | | | phosphate.** | +-----------------------------------+-----------------------------------+ | **Effect** | Inorganic phosphate released | +-----------------------------------+-----------------------------------+ | **Regulators** | Activation: high levels of ATP | | | | | | Inhibition: high levels of AMP, | | | [fructose | | | 2,6-bisphosphate] | +-----------------------------------+-----------------------------------+ | **Other info** | (PFK-1) enzyme - catalyses the | | | reverse reaction: [fructose | | | 2,6-bisphosphate] | | | activates it | | | | | | - | | | | | | Thus [fructose | | | 2,6-bisphosphate] - | | | during well fed state | | | | | | - | +-----------------------------------+-----------------------------------+ Note: Fru-2,6-BP is synthesised by PFK-2 +-----------------------------------+-----------------------------------+ | **\]** | **[PFK-2]** | +===================================+===================================+ | **Reaction** | **1\] Fructose 6-phosphate + ATP | | | → Fructose 2,6-bisphosphate + ADP | | | (kinase)** | | | | | | **2\] Fructose 2,6-bisphosphate → | | | Fructose 6-phosphate + Pi | | | (phosphatase)​** | +-----------------------------------+-----------------------------------+ | **Effect** | Has 2 functions: | | | phosphofructokinase activity and | | | fructose-2,6-bisphosphatase | | | activity. | +-----------------------------------+-----------------------------------+ | **Regulators** | Hormone regulation: | | | | | | Insulin downregulates | | | (dephosphorylates) \[2\] - | | | activating glycolysis, inhibiting | | | gluconeogenesis | | | | | | Glucagon upregulates | | | (phosphorylates) \[2\] - | | | inhibiting glycolysis, activating | | | gluconeogenesis | | | | | | Liver PFK-2 is inhibited by | | | phosphorylation (favouring | | | gluconeogenesis). | | | | | | Muscle PFK-2 is unaffected or | | | even activated by | | | phosphorylation, allowing | | | glycolysis to continue for | | | energy, especially in cardiac | | | muscle. | +-----------------------------------+-----------------------------------+ | **Other info** | Reversible reaction | +-----------------------------------+-----------------------------------+ **REACTION 3: Dephosphorylation of glucose 6-phosphate** +-----------------------------------+-----------------------------------+ | **\]** | **[Glucose | | | 6-phosphatase]** | +===================================+===================================+ | **Reaction** | **Glucose 6-phosphate → Glucose** | +-----------------------------------+-----------------------------------+ | **Effect** | Free glucose that can be released | | | into the bloodstream. (only liver | | | and kidney) | +-----------------------------------+-----------------------------------+ | **Regulators** | | +-----------------------------------+-----------------------------------+ | **Other info** | Final step of gluconeogenesis. | | | | | | This reaction bypasses the | | | irreversible | | | glucokinase/hexokinase reaction. | +-----------------------------------+-----------------------------------+ 8\] Pentose phosphate pathway - Fructose and galactose pathway ============================================================== Fructose metabolism **\]** **[Fructokinase]** ---------------- ------------------------------------------ **Reaction** **Fructose → Fructose 1-phosphate** **Effect** ATP used **Regulators** **Other info** Deficiency: causes Essential fructosuria +-----------------------------------+-----------------------------------+ | **\]** | **[Aldolase B]** | +===================================+===================================+ | **Reaction** | **Fructose 1-phosphate → | | | Glyceraldehyde/ | | | Dihydroxyacetone** | +-----------------------------------+-----------------------------------+ | **Other info** | aldolase B - liver | | | | | | Part of fructose degradation | | | | | | Deficiency: causes Hereditary | | | fructose intolerance | +-----------------------------------+-----------------------------------+ +-----------------------------------+-----------------------------------+ | **\]** | **[Aldolase A]** | +===================================+===================================+ | **Reaction** | **Fructose 1,6-bisphosphate → | | | Glyceraldehyde 3-phosphate/ | | | Dihydroxyacetone** | +-----------------------------------+-----------------------------------+ | **Other info** | aldolase A - muscle and RBC | | | | | | Part of fructose degradation | +-----------------------------------+-----------------------------------+ **Polyol pathway** Synthesis of fructose from glucose Glucose → reduced to sorbitol (sugar) → oxidised to fructose +-----------------------------------+-----------------------------------+ | **\]** | **[Aldose | | | Reductase]** | +===================================+===================================+ | **Reaction** | **Glucose → Sorbitol** | +-----------------------------------+-----------------------------------+ | **Effect** | NADPH + H+ → NADP+ | +-----------------------------------+-----------------------------------+ | **Regulators** | | +-----------------------------------+-----------------------------------+ | **Other info** | Glucose in cell - converted to | | | sorbitol - sorbitol cannot pass | | | through membranes - builds up | | | | | | Sorbitol accumulation causes → | | | Cataract formation, Peripheral | | | neuropathy, Vascular problems | +-----------------------------------+-----------------------------------+ **\]** **[Sorbitol dehydrogenase]** ---------------- ------------------------------------------------------------------------- **Reaction** **Sorbitol → Fructose** **Effect** NAD+ → NADH + H+ **Regulators** **Other info** In liver this offers a pathway to go into glycolysis or gluconeogenesis **Galactose metabolism** Galactose to lactose and glucose **\]** **[Galactokinase]** ---------------- ------------------------------------------------------------------------------------------------------ **Reaction** **Galactose → Galactose 1-P** **Effect** ATP →ADP **Regulators** **Other info** Galactokinase deficiency: autosomal disorder leading to accumulation of galactose in blood and urine +-----------------------------------+-----------------------------------+ | **\]** | **[Galactose 1-P | | | uridyltransferase]** | +===================================+===================================+ | **Reaction** | **Galactose 1-P + UDP-Glucose → | | | UDP-galactose + Glucose 1-P** | +-----------------------------------+-----------------------------------+ | **Effect** | Exchange of P and UDP | +-----------------------------------+-----------------------------------+ | **Regulators** | | +-----------------------------------+-----------------------------------+ | **Other info** | Classic Galactosemia: | | | Uridyltransferase deficiency - | | | causes galactosemia, | | | galactosuria, vomiting, diarrhea | | | and jaundice. | | | | | | Accumulation of Galactose 1-P and | | | galactitol in nerves, lever, and | | | kidney causes damage as well. | | | | | | Newborn screening is available, | | | | | | Therapy: removal of galactose | | | (lactose) from the diet | | | | | | Note: females at risk of | | | premature ovarian failure. | +-----------------------------------+-----------------------------------+ **The role of NADPH in the RBC** **\]** **[Glucose 6-P dehydrogenase]** ---------------- ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- **Reaction** **Glucose 6-P + NADP+ → 6-phosphogluconate + NADPH + H+ (in RBC)** **Effect** NADPH produce oxidised again to NADP+ → this is used to ultimately remove reactive oxygen species (ROS) **Regulators** **Other info** Thus: **[Glucose 6-P dehydrogenase]** deficiency or NADP deficiency causes an increase in ROS and heinz body aggregation → these cause mechanical stress in the RBC and thus leads to hemolytic anaemia. 9\] Fatty acid oxidation ======================== +-----------------------------------+-----------------------------------+ | **\]** | **[Lipase]** | +===================================+===================================+ | **Reaction** | **Triacylglycerol → | | | Diacylglycerol + Fatty acid** | +-----------------------------------+-----------------------------------+ | **Effect** | Free fatty acid released | +-----------------------------------+-----------------------------------+ | **Regulators** | Hormone regulation: Insulin | | | downregulates | | | | | | - | | | | | | | | | | | | - | +-----------------------------------+-----------------------------------+ | **Other info** | Releases fatty acids from | | | triacylglycerols | +-----------------------------------+-----------------------------------+ **Carnitine shuttle** **\]** **[Carnitine palmitoyl transferase I]** ---------------- --------------------------------------------------------------------------------------------------------------- **Reaction** **Fatty acyl CoA + carnitine → CoA + acylcarnitine** **Effect** Acyl gp of the fatty acid can be transported from the intramembranous space to the inside of the mitochondria **Regulators** **Other info** Enzyme found on the outer mitochondrial membrane **\]** **[Carnitine palmitoyl transferase II]** ---------------- ------------------------------------------------------------------- **Reaction** **CoA + acylcarnitine → Fatty acyl CoA + Carnitine** **Effect** Reforms the fatty acyl CoA, this time in the mitochondrial matrix **Regulators** **Other info** Enzyme found on the inner mitochondrial membrane **Beta oxidation** +-----------------------------------+-----------------------------------+ | **\]** | **[Acetyl CoA | | | carboxylase]** | +===================================+===================================+ | **Reaction** | **Acetyl CoA → Malonyl CoA** | +-----------------------------------+-----------------------------------+ | **Effect** | CO2 used, ATP→ADP | +-----------------------------------+-----------------------------------+ | **Regulators** | Coenzyme: Biotin | | | | | | Activation: Citrate | | | | | | Inhibition: Long chain fatty acyl | | | CoA, Palmitate (Product of fatty | | | acid synthesis) | | | | | | Hormonal regulation: Insulin - | | | Well fed state - activates ACC | | | (liver) | | | | | | - | | | | | | Note: diet - long term high carb | | | - upragulates (for farry acid syn | | | and thus storage) | +-----------------------------------+-----------------------------------+ | **Other info** | **2 functions** | | | | | | 1\] First and rate limiting step | | | - in fatty acid synthesis | | | | | | When active - fatty acid syn - | | | increases triacylglycerol storage | | | in adipose | | | | | | When inactive - fatty acid | | | oxidation - increase fatty acid | | | release in blood | | | | | | [2\] Used to create Malonyl CoA | | | which inhibits precursor for B | | | oxidation] | +-----------------------------------+-----------------------------------+ Final product of B oxidation is Acetyl CoA - **Oxidation of ketone bodies** 3 steps - produces 2 Acetyl CoA to enter into TCA cycle **\]** **[β-hydroxybutyrate dehydrogenase.]** ---------------- ------------------------------------------------------------------------------------------ **Reaction** **β-hydroxybutyrate → Acetoacetate** **Effect** Produces NADH. **Regulators** **Other info** Reversible reaction - last step of ketone body formation, first step of ketone oxidation **\]** **[Succinyl CoA acetoacetate CoA transferase]** ---------------- --------------------------------------------------------------------------- **Reaction** **Acetoacetate → Acetoacetyl CoA (step2)** **Effect** HS-CoA used **Regulators** **Other info** This enz not present in liver - thus ketone oxidation does not occur here +-----------------------------------+-----------------------------------+ | **\]** | **[Thiolase ]** | +===================================+===================================+ | **Reaction** | **Acetoacetyl-CoA → 2 | | | Acetyl-CoA** | +-----------------------------------+-----------------------------------+ | **Effect** | CoA-ASH used - Acetyl AoA | | | produces | +-----------------------------------+-----------------------------------+ | **Regulators** | | +-----------------------------------+-----------------------------------+ | **Other info** | Acetyl-CoA enters the **TCA | | | cycle** for energy production. | | | | | | REversible reaction: first step | | | of ketone body formation, last | | | step of ketone oxidation | +-----------------------------------+-----------------------------------+ 10\] Fatty acid and triacylglycerol synthesis ============================================= **Fatty acid synthesis** +-----------------------------------+-----------------------------------+ | **\]** | **[Acetyl CoA | | | carboxylase]** | +===================================+===================================+ | **Reaction** | **Acetyl CoA → Malonyl CoA** | +-----------------------------------+-----------------------------------+ | **Effect** | CO2 used, ATP→ADP | +-----------------------------------+-----------------------------------+ | **Regulators** | Coenzyme: Biotin | | | | | | Activation: Citrate | | | | | | Inhibition: Long chain fatty acyl | | | CoA, Palmitate (Product of fatty | | | acid synthesis) | | | | | | Hormonal regulation: Insulin - | | | Well fed state - activates ACC | | | (liver) | | | | | | - | | | | | | Note: diet - long term high carb | | | - upragulates (for farry acid syn | | | and thus storage) | +-----------------------------------+-----------------------------------+ | **Other info** | **2 functions** | | | | | | [1\] First and rate limiting step | | | - in fatty acid | | | synthesis] | | | | | | When active - fatty acid syn - | | | increases triacylglycerol storage | | | in adipose | | | | | | When inactive - fatty acid | | | oxidation - increase fatty acid | | | release in blood | | | | | | 2\] Used to create Malonyl CoA | | | which inhibits precursor for B | | | oxidation | +-----------------------------------+-----------------------------------+ **\]** **[Fatty acid synthase]** ---------------- -------------------------------------------------------------------------------- **Reaction** **Acetyl CoA + Malonyl CoA \[x7\] → Palmitic acid (16C fatty acid chain)** **Effect** NADPH + H+ → NADP+, H20 and CO2 released (these happen only in some reactions) **Regulators** **Other info** Elongation of the fatty acid chain **Triacylglyceride synthesis** +-----------------------------------+-----------------------------------+ | **\]** | **[Glycerol Kinase]** | +===================================+===================================+ | **Reaction** | **Glycerol → Glycerol-3-P | | | (liver)** | +-----------------------------------+-----------------------------------+ | **Effect** | ATP→ADP | +-----------------------------------+-----------------------------------+ | **Regulators** | | +-----------------------------------+-----------------------------------+ | **Other info** | Step 1 of Triacylglyceride | | | synthesis | | | | | | This only takes place in the | | | liver - in adipose tissue and | | | some liver: | | | | | | - | | | | | | From Glycerol 3-P → goes down 3 | | | reactions to form Triacylglycerol | +-----------------------------------+-----------------------------------+ +-----------------------------------+-----------------------------------+ | **\]** | **[Glycerol 3-phosphate | | | dehydrogenase]** | +===================================+===================================+ | **Reaction** | **Dihydroxyacetone (DHAP) → | | | Glycerol 3-P** | +-----------------------------------+-----------------------------------+ | **Effect** | NADH → NAD+ | +-----------------------------------+-----------------------------------+ | **Regulators** | | +-----------------------------------+-----------------------------------+ | **Other info** | This reactions takes place in | | | both Liver and Adipose tissue | | | | | | Note: in liver above reaction | | | also takes place | +-----------------------------------+-----------------------------------+ 11\] Alcohol metabolism ======================= +-----------------------------------+-----------------------------------+ | **\]** | **[Alcohol dehydrogenase | | | (ADH)]** | +===================================+===================================+ | **Reaction** | **Ethanol → Acetaldehyde** | +-----------------------------------+-----------------------------------+ | **Effect** | NAD+ → NADH+ H+ | +-----------------------------------+-----------------------------------+ | **Regulators** | | +-----------------------------------+-----------------------------------+ | **Other info** | Pathway 1 | | | | | | Note: ADH and MEOS are coenzymes. | | | | | | At low ethanol concs, ADH is most | | | imp due to its lower Km compared | | | to MEOS. | +-----------------------------------+-----------------------------------+ +-----------------------------------+-----------------------------------+ | **\]** | **[CYP2E1]** | +===================================+===================================+ | **Reaction** | **Ethanol → Acetaldehyde** | +-----------------------------------+-----------------------------------+ | **Effect** | Forms NADP+ and H2O | +-----------------------------------+-----------------------------------+ | **Regulators** | Activation: High alcohol | | | consumption | +-----------------------------------+-----------------------------------+ | **Other info** | Pathway 2 - Used in excess | | | alcohol concentrations → can lead | | | to ROS and complications | | | | | | variation in isoenzymes | | | →variation in susceptibility of | | | alcohol induced liver disease. | +-----------------------------------+-----------------------------------+ +-----------------------------------+-----------------------------------+ | **\]** | **[acetaldehyde dehydrogenase | | | ALDH]** | +===================================+===================================+ | **Reaction** | **Acetaldehyde → acetate** | +-----------------------------------+-----------------------------------+ | **Effect** | NAD+ → NADH+ H+ | +-----------------------------------+-----------------------------------+ | **Regulators** | Variant: ALDH2\*2 variant results | | | in high Km (low affinity) and low | | | Vmax (reduced capacity) → Leads | | | to accumulation of acetaldehyde. | | | | | | Inhibition: Disulfiram → | | | inhibitor used to treat | | | alcoholism - by increasing toxic | | | acetaldehyde and thus causing | | | unpleasant effects. | +-----------------------------------+-----------------------------------+ | **Other info** | Acetate then goes into | | | circulation - ALDH 1 is | | | cytosolic, ALDH 2 is | | | mitochondrial | | | | | | ALDH 2 has a low Km and high | | | specificity for acetaldehyde | | | | | | NAD+ required → Thus if slow | | | regeneration of NAD+ → | | | acetaldehyde accumulates in the | | | liver and enters the bloodstream | | | (ex. malfunctioning - malate | | | aspartate shuttle) | +-----------------------------------+-----------------------------------+ +-----------------------------------+-----------------------------------+ | **\]** | **[Acetyl CoA | | | synthetase]** | +===================================+===================================+ | **Reaction** | **Acetate → acetyl CoA** | +-----------------------------------+-----------------------------------+ | **Effect** | ATP→AMP | +-----------------------------------+-----------------------------------+ | **Regulators** | CoASH needed | | | | | | Hormone regulation: Insulin | | | upregulates (dephosphorylates) → | | | fatty acid usage and storage | +-----------------------------------+-----------------------------------+ | **Other info** | | +-----------------------------------+-----------------------------------+ +-----------------------------------+-----------------------------------+ | **\]** | **CYP2E2** | +===================================+===================================+ | **Reaction** | **Oxidation of a drug or | | | xenobiotic** | +-----------------------------------+-----------------------------------+ | **Effect** | | +-----------------------------------+-----------------------------------+ | **Regulators** | Inhibition: Ethanol | +-----------------------------------+-----------------------------------+ | **Other info** | Ethanol inhibits CYP2B2→ | | | (activates phenobarbital) | | | | | | CYP2B2 inactivates phenobarbital | | | - Leads to drug tolerance. | +-----------------------------------+-----------------------------------+ **Phenobarbital** is a drug that calms the brain, helps with seizures, and promotes sleep by boosting the effect of a brain chemical called GABA. 12\] Amino Acid metabolism - transamination and the urea cycle ============================================================== **[From AA → Urea]** **Transamination** **\]** **[Aspartate aminotransferase]** -------------- ------------------------------------------------------------ **Reaction** **Aspartate + α-Ketoglutarate ⇌ Oxaloacetate + Glutamate** **Effect** Transamination - and production of glutamate (reversible) **\]** **[Alanine aminotransferase]** -------------- ----------------------------------------------------------- **Reaction** **Alanine + α-Ketoglutarate ⇌ Pyruvate + Glutamate** **Effect** Transamination - and production of glutamate (reversible) +-----------------------------------+-----------------------------------+ | **\]** | **[Glutamate | | | dehydrogenase]** | +===================================+===================================+ | **Reaction** | **A-ketoglutarate ⇌ Glutamate** | +-----------------------------------+-----------------------------------+ | **Effect** | NH4+ released or used, NADP → | | | NADPH | +-----------------------------------+-----------------------------------+ | **Regulators** | | +-----------------------------------+-----------------------------------+ | **Other info** | This reaction is reversible In | | | Muscle and peripheral tissue | | | forward reaction, | | | | | | In liver backward reaction - to | | | release NH4 for urea cycle | | | | | | Thus at the start and end of the | | | pathway. | +-----------------------------------+-----------------------------------+ +-----------------------------------+-----------------------------------+ | **\]** | **[Glutamine | | | synthetase]** | +===================================+===================================+ | **Reaction** | **glutamate + ammonia → | | | glutamine** | +-----------------------------------+-----------------------------------+ | **Effect** | Glutamine formed | +-----------------------------------+-----------------------------------+ | **Regulators** | | +-----------------------------------+-----------------------------------+ | **Other info** | Glutamine formed - can be | | | transported from peripheral | | | tissues to liver | | | | | | Typical pathway in muscle and | | | peripheral cell: a-KG → glutamate | | | → glutamine | +-----------------------------------+-----------------------------------+ **\]** **[Glutaminase]** ---------------- ------------------------------------------------------------------------------------- **Reaction** **glutamine → NH4+ + glutamate** **Effect** Glutamate regenerated, NH4+ released. **Regulators** **Other info** NH4+ released, first of the 2 NH4+ released, The second comes from Glutamate → a-KG **Regulation of the urea cycle** **\]** **[Carbamoyl phosphate synthase]** ---------------- -------------------------------------------------------------------------------------------- **Reaction** **CO2 + NH3 → Carbamoyl phosphate** **Effect** 2ATP used **Regulators** Activation: N-acetylglutamate - formed after high protein meal from Acetyl CoA + glutamate **Other info** First reaction of urea cycle 13\] Amino acid carbon skeleton =============================== **\]** **[Glutaminase]** -------------- --------------------------------------------- **Reaction** **Glutamine → glutamate** → a-ketoglutarate **\]** **[Hidtidase]** -------------- ----------------------------------------------------------------- **Reaction** **Histidine → FIGLU** → Glutamate → glutamate → a-ketoglutarate **\]** **[Alanine aminotransferase]** -------------- -------------------------------------------- **Reaction** **alanine → pyruvate** **\]** **[Serine dehydratase]** -------------- -------------------------------------- **Reaction** **serine → pyruvate** **\]** **[Phenylalanine hydroxylase]** -------------- ---------------------------------------------------------- **Reaction** **Phenylalanine → tyrosine** → fumarate and acetoacetate 14\] Biosynthesis of amino acids ================================ 15\] Purine and pyrimidine Metabolism ===================================== Coenzymes ========= Deficiencies ============