SF.45 HMP Shunt and RBC Metabolism PDF

HMP Shunt and Red Blood Cells Metabolism Geri Deevska, PhD Fall 2024 Contact info: office #310C [email protected] Biochemistry Genetics 1  Session Outline 1. Overview of RBC metabolism 2. Glycol...

HMP Shunt and Red Blood Cells Metabolism Geri Deevska, PhD Fall 2024 Contact info: office #310C [email protected] Biochemistry Genetics 1  Session Outline 1. Overview of RBC metabolism 2. Glycolysis: Energy production 2,3-BPG production Reduction of Fe3+ to Fe2+ Clinical correlates 3. Pentose Phosphate Pathway (HMP shunt) Reactions and products NADPH biological functions Clinical correlates 2  Session Objectives 1. Summarize all important aspects of RBC’s energy metabolism and explain the role of 2,3-BPG. 2. Describe the metabolic roles of the Pentose phosphate pathway (PPP, HMP shunt) in RBC and summarize its stages. 3. Compare and contrast NADPH and NADH and explain the role of NADPH in RBC. 4. Identify the underlying biochemical causes of the major metabolic disorders affecting RBC and describe the respective consequences for human health. 3 RBC Overview *know characteristics of RBCs, esp. immature vs mature immature RBC = larger, lots of organelles, big nucleus** **can RBCs use fatty acids for energy? - no, because they have no mitochondria ✓ Function - transport of oxygen from lungs to tissues - only get energy via glycolysis ✓ Structure: ‣ Lack nucleus and membrane-bond cellular organelles ‣ Shaped as biconcave disc to maximize the cell surface for gas exchange Bone marrow ‣ Extremely flexible to pass through narrow capillaries ✓ Short life-span ~ 120 days ✓ Fast turnover -10 12 RBC produced daily Blood mature RBC = smaller, no organelles, no nucleus** Modified from: Figure 10.22 and Figure 10.3, Chapter 10: Blood 4 Histology: A Text and Atlas with Correlated Cell and Molecular Biology, 7e RBC Metabolism Overview only 2 ATP molecules produced in glycolysis Pathways ✓ Glycolysis ‣ Synthesis of ATP ‣ Production of 2,3 BPG ‣ Reduction of Fe3+ to Fe2+ O2 can only attach to Fe2+ ✓ Pentose phosphate pathway (PPP) or hexose monophosphate shunt (HMP shunt) ‣Role of NADPH in RBC Modified from: Figure 42.1 5 Chapter 42: “Marks’ Basic Med. Biochem.”, 6e  Session Outline 1. Overview of RBC metabolism 2. Glycolysis: Energy production 2,3-BPG production Reduction of Fe3+ to Fe2+ Clinical correlates 3. Pentose Phosphate Pathway (HMP shunt) Reactions and products NADPH biological functions Clinical correlates 6 RBC Energy Metabolism no mitochondria in RBCs, so has to be anaerobic only way to produce ATP in RBCs Anaerobic glycolysis: investing Energy ✓ For 1 glucose: ‣ 2 ATP net energy yield ‣ 2 NADH ‣ 2 Pyruvate ✓ NAD+ is regenerated through lactate production ✓ Lactate - send to the liver (Cori cycle) Energy harvesting Pyruvate kinase Modified from: Figure 42.1 7 Chapter 42: “Marks’ Basic Med. Biochem.”, 6e Glucose Transporters: GLUT 1 ‣ GLUT proteins span RBCs only use glucose the PM ‣ Facilitated diffusion: ATP- independent ‣ Upon glucose binding it changes conformation, which allows transport across the membrane ‣ Tissue specific expression ‣ Specific regulation and affinity ‣ Specificity for substrate Modified from: Table 21.5, Chapter 21: “Marks’ Basic Med. Biochem.”, 6e 8 RBC Energy Metabolism Anaerobic glycolysis: investing Energy ✓ For 1 glucose: ‣ 2 ATP net energy yield ‣ 2 NADH ‣ 2 Pyruvate ✓ NAD+ is regenerated through lactate production ✓ Lactate - send to the liver (Cori cycle) Energy harvesting Pyruvate kinase Modified from: Figure 42.1 9 Chapter 42: “Marks’ Basic Med. Biochem.”, 6e RBC Energy Metabolism with PK deficiency, lifespan of RBC is shortened - ATP production is cut in half because of lack of the enzyme (patient will have a lot less energy) Anaerobic glycolysis: 2 enzymes for energy production investing in RBCs: Energy - Pyruvate kinase ✓ For 1 glucose: - G6PD ‣ 2 ATP net energy yield ‣ 2 NADH ‣ 2 Pyruvate ✓ NAD+ is regenerated through lactate production RBCs produce their own type of pyruvate kinase - when it's deficient, results in hemolytic anemia ✓ Lactate - send to the liver (Cori cycle) Energy harvesting Clinical Correlation: Pyruvate kinase deficiency ‣ Results in hemolytic anemia (nonspherocytic) ‣ Symptoms - fatigue, unusually pale skin, shortness of breath, jaundice, increases the risk of developing gall Pyruvate stones kinase ‣ The second most common one after G6PD deficiency ‣ Can be distinguished from G6PD deficiency by lack of G6PD deficiency = msot common deficiency that leads to hemolytic anemia Heinz bodies (precipitated hemoglobin) pyruvate kinase deficiency = 2nd most common Modified from: Figure 42.1 10 Chapter 42: “Marks’ Basic Med. Biochem.”, 6e 2,3 BPG Production in RBC 2,3 -BPG = most abundant phosphate molecule in RBCs 2,3 Bisphosphoglycerate (2,3-BPG): an important metabolite in glycolysis* ✓ Allosteric regulator of O2 binding to Hb ✓ The most abundant organophosphate in RBC ✓ Rapidly degraded in blood stored for transfusion ✓ Increased in adapting to high altitudes Modified from: Figure 3.11, Chapter 3: Modified from: Figure 42.1 11 Lippincott’s Ills. Reviews: Biochem.”, 7e Chapter 42: “Marks’ Basic Med. Biochem.”, 6e RBC Reduction of Fe3+ to Fe2+ Pathways ✓ Glycolysis ‣ Synthesis of ATP ‣ Production of 2,3 BPG ‣ Reduction of Fe3+ to Fe2+ Modified from: Figure 42.1 12 Chapter 42: “Marks’ Basic Med. Biochem.”, 6e Heme and Hemoproteins Heme structure Prosthetic group Lippincott’s Ills. Reviews: Biochem.”, 8e Modified from: Figure 3.1, Chapter 3: Protein chain Hemoprotein Redox state of Fe Function Hemoglobin Fe2+ O2 transport in blood has to stay Fe2+ to bind O2* Myoglobin Fe2+ O2 storage in muscle A porphyrin cyclic molecule: these carry electrons, ‣ Four pyrrole rings joined Cytochrome Fe2+ Fe3+swtich from reducedETC to oxidized state via methenyl bridges ‣ A metal ion - iron (ferrous Cyt P450 Fe2+ Fe3+ Hydroxylation Fe2+ or ferric Fe3+) Catalase Fe2+ Fe3+ Degradation of H2O213 Heme Iron Oxidation Clinical Correlation: Lippincott Illustrated Reviews: Biochemistry”, 8e Methemoglobinemia: Oxidation Reduction “Chocolate cyanosis” - blue Modified from: Figure 3.22 Chapter 3: coloration of the skin and mucous membranes and can cause brown-colored blood as a result of the dark-colored methemoglobin. Babies have half the capacity to reduce metHb -> more prone to oxidation* Symptoms: related to the Unable to bind O2 degree of tissue hypoxia and 70% 30% Normal include anxiety, headache, and dyspnea rarely coma and Methemoglobinemia death when MetHb is more than 70% Treatment: methylene blue ( a reducing agent) 14 Methemoglobinemia Types Methemoglobinemia Acquired Congenital ‣ Oxidative stress ‣ Deficiency of NADH- ‣ Certain drugs and/or cytochrome b5 the reductase that maintains iron in its 2+ state their metabolites causing reductase inability to maintain iron ‣ Mutations in the α- or β- in its Fe2+ state globin chain producing abnormal HbM resistant to the reductase (rare) 15 The “Kentucky Blue People” Clinical Correlation: Deficiency of NADH-cytochrome b5 reductase Painting of the family of Martin and Mary Fugate ‣ Autosomal recessive disorder who settled near Hazard, KY and had 7 children. ‣ Close relative mating !!! Father - blue (homozygous) Mother - carrier (heterozygous) 16  Session Outline 1. Overview of RBC metabolism 2. Glycolysis: Energy production 2,3-BPG production Reduction of Fe3+ to Fe2+ Clinical correlates 3. Pentose Phosphate Pathway (HMP shunt) Reactions and products NADPH biological functions Clinical correlates 17 HMP Shunt Oxidative Reactions Chapter 27: “Marks’ Basic Med. Biochem.”, 6e Oxidative ✓ 3 irreversible steps - produce NADPH ✓ Rate-limiting committed step: ‣ Glucose 6-phosphate dehydrogenase Modified from: Figure 27.1 (G6PD) Inhibitors: NADPH (competitively) Activators: insulin stimulates G6PD expression Hexose MonoPhosphate shunt (HMP shunt) 18 HMP Shunt Oxidative Reactions Chapter 27: “Marks’ Basic Med. Biochem.”, 6e Oxidative ✓ 3 irreversible steps - produce NADPH ✓ Rate-limiting step: ‣ Glucose 6-phosphate dehydrogenase Modified from: Figure 27.1 (G6PD) Nonoxidative Reactions ✓ Reversible steps Nonoxidative ✓ Interconvert sugars with 3 to 7 C-atoms final product ✓ Enzymes: (sugar molecule to be used in ‣ Transaldolase nucleotide synthesis) ‣ Transketolase thiamine deficiency will affect transketolase* requires TPP (from thiamine, vit. B1) important in diagnosis of thiamine deficiency done by measurement of its activity 19 Hexose MonoPhosphate shunt (HMP shunt) in RBCs HMP Shunt “Lippincott’s Ills. Reviews: Biochem.”, 8e Modified from: Figures 13.2, Chapter 13: don't need to remember all the names, just the nonoxidative rxns are reversible* 20 Cellular Needs Determine HMP Shunt Direction each one of these parts of the pathway can run independently of each other, depending on the needs of the cell 21 NADP+ and NADPH (Review) Niacin only difference between NADH and NADPH is the phosphate group - means NADPH can't donate its electrons to the ETC (only NADH can) (Vitamin B3) Clinical correlation: Pellagra A deficiency of niacin: a disease involving the skin, gastrointestinal tract, and CNS. The symptoms of pellagra progress through the three Ds: dermatitis (photosensitive), diarrhea, and dementia. If untreated, death (a fourth D) occurs. 22 NADPH Biological Roles ✓ Electron donor for the biosynthesis of: NADPH is used as an electron donor in biosynthetic rxns ‣ Fatty acids ‣ Cholesterol ‣ Steroids ✓ Electron donor for the neutralization of reactive oxygen species (ROS): ‣ Hydrogen peroxide (H2O2) these are harmful to us if not neutralized ‣ Superoxide (O 2− ) ‣ Hydroxyl radical (OH ) ✓ Provides reducing equivalents for Cytochrome P450 monooxygenase system: ‣ Biosynthesis of steroids ‣ Detoxification of xenobiotics and drugs ✓ Play role in phagocytosis - destruction of pathogens by macrophages and neutrophils ✓ Substrate for the synthesis of nitric oxide (NO) 23 NADPH Role in RBC RBCs need to be able to neutralize free radicals - will do so by using GSH Glutathione (GSH) reduced glutathione reductase uses the electrons from NADPH (which is produced by RBCs from the Pentose phosphate pathway reduced NADPH oxidized The ONLY source of NADPH in RBC Modified from: Figure 25.13 Chapter 27: “Marks’ Basic Med. Biochem.”, 6e 24 G6PD Deficiency if G6PD deficient, then Precipitating Chapter 27: “Marks’ Basic Med. Biochem.”, 6e Modified from: Figure 27.7 not enough NADPH resulting in oxidation, leading to formation of factors: Heinz bodies (eventually hemolysis) - patients are asymptomatic until they get an infection or take a new medication (resulting in oxidative stress in their RBCs) reduced oxidized Clinical Correlation: G6PD deficiency ‣ Episodic hemolytic anemia induced by oxidative stress ‣ RBC contain Heinz bodies (precipitated hemoglobin) ‣ One of the most common single gene disorders ‣ X-linked (males affected predominantly) 25 G6PD Deficiency Variants and Hemolysis G6PD genetics: ✓High degree of population specific polymorphism ✓More than 400 putatively distinct G6PD variants identified ✓More than 200 mutations most are point missense ✓Mutations result in alter enzyme kinetics by affecting: >60% activity of the enzyme = asymptomatic ‣ E stability (majority of