BMSC 230 - Metabolism (Chapter 18) PDF

BMSC 230 - Metabolism TOPICS Pyruvate Dehydrogenase (Chapter 18) Citric Acid Cycle (Chapter 19) Electron Transport/Oxidative Phosphorylation (Chapter 20, 21) Lipid Metabolism – degradation and synthesis (Chapter 27, 28, 29) Dr. Scot Stone Dept of Biochemistry Office: 2D30.5 Health Sciences Bldg 966-...

BMSC 230 - Metabolism TOPICS Pyruvate Dehydrogenase (Chapter 18) Citric Acid Cycle (Chapter 19) Electron Transport/Oxidative Phosphorylation (Chapter 20, 21) Lipid Metabolism – degradation and synthesis (Chapter 27, 28, 29) Dr. Scot Stone Dept of Biochemistry Office: 2D30.5 Health Sciences Bldg 966-4217 [email protected] 1 Metabolic Pathways Are Integrated 2 Tymoczko Berg Stryer Biochemistry: A Short Course 4th Edition CHAPTER 18 Preparation for the Citric Acid Cycle Pyruvate Dehydrogenase complex (PDH) © 2013 W. H. Freeman and Company Cellular Respiration: “The metabolic reactions in an organism that produce energy from nutrients” 3 Stages: 1. Acetyl CoA synthesis 2. Citric acid cycle 3. Electron transfer/oxidative phosphorylation Energy: Adenosine Triphosphate (ATP) “energy currency” Nitrogenous base (Adenine) Sugar (Ribose) 4 Acetyl CoA: metabolic "receiving and shipping department" for all classes of biomolecules and is a major source of metabolic energy. Fatty Acids Amino Acids Glucose Acetyl-CoA Cholesterol Fatty Acids ATP 5 Pyruvate Dehydrogenase Complex (PDH) catalyzes the synthesis of Acetyl-CoA in the mitochondria: Present in the mitochondria Catalyzes 5 reactions: pyruvate → Acetyl CoA (NADH + CO2) Pyruvate E2 Dihydrolipoyl Transacetylase E1 Pyruvate Dehydrogenase E3 Dihydrolipoyl Dehydrogenase Acetyl CoA + CO2+ NADH What is the advantage of using a protein complex? 6 MPC – Mitochondrial pyruvate transporter Glucose Pyruvate Glycolysis MPC Pyruvate Pyruvate Dehydrogenase Complex (PDH) PDH complex: 3 enzymes → catalyze 5 biochemical reactions Requires 5 cofactors oxidative decarboxylation Irreversible reaction CO2 + acetyl CoA CANNOT re-form pyruvate 8 Pyruvate Dehydrogenase Complex Requires 5 Cofactors Cofactors: helper molecules non-protein can be bound to an enzyme (either tightly or loosely) required for catalysis do not catalyse reactions PDH Cofactors: 1. Thiamine Pyrophosphate (TPP) 2. Lipoic Acid 3. Coenzyme A 4. FAD (flavin adenine dinucleotide) → electron carrier 5. NAD+ (nicotinamide adenine dinucleotide ) → electron carrier 9 Thiamine Pyrophosphate (TPP) TPP is derived from vitamin B1 (thiamine) Tightly bound to E1 of PDH accepts 2 carbon backbone of acetyl CoA after decarboxylation of pyruvate hydroxyethyl TPP intermediate TPP → “transient carbon carrier” 10 Lipoic Acid Lysine Lysine Lysine Tightly bound cofactor of E2 subunit → lipoyl group (8 carbon chain) 2 thiol groups → oxidized, reduced, acetylated carries electrons and acyl (carbon) groups accepts hydroxyethyl intermediate from TPP as an acetyl group 11 Coenzyme A/Acetyl Coenzyme A Coenzyme A Thioester bond O CH3-C Acetyl Coenzyme A NADH and FADH2 Electron carriers Exist in oxidized or reduced states Carry 2 electrons NADH - mobile electron carrier NAD+(ox) + 2e- + 2H+ → NADH(red) + H+ FADH2 – protein bound electron carrier FAD(ox) + 2e- + 2H+ → FADH2(red) 13 Mammals have 60 E2 Reactions of the Pyruvate Dehydrogenase Complex Rxn 1 (E1) Rearrangement Rxn 2 (E1) Rxn 5 (E3) Rxn 4 (E3) Rxn 3 (E2) What is the advantage of using a protein complex? 5 reaction sequence is an example of SUBSTRATE CHANNELING Local concentration of substrates around enzymes is kept high Rate of reaction is not limited by diffusion of substrates to each subunit of PDH Efficient Inefficient Pyruvate Pyruvate Acetyl CoA Acetyl CoA 16 Summary of PDH and synthesis of Acetyl CoA 2 E3 E3 E1 E1 E2 Summary of PDH and synthesis of Acetyl CoA Pyruvate is converted to acetyl CoA by PDH complex PDH: 3 enzymes and 5 cofactors (coenzymes/prosthetic groups) E1: oxidative decarboxylation of pyruvate and transfer of 2 carbon unit (hydroxyethyl intermediate) to E2. E2: transfer of acetyl group to CoA to synthesize Acetyl CoA. E3: regenerates oxidized lipoyl group of E2 and transfers protons and electrons first to FAD and then to NAD+ to complete the reaction cycle. Overall: Glucose 2 Pyruvate 2 Acetyl CoA + 2 NADH + 2 CO2 eTCA Cycle e- Ox/Phos ATP Regulation of Acetyl CoA Synthesis by energy charge Regulation of pyruvate dehydrogenase by phosphorylation/dephosphorylation P PDH Kinase Phosphatase PDH Pyruvate Inactive Active Acetyl CoA + CO2 Sufficient energy supply:  ATP, acetyl CoA, NADH PDH kinase → phosphorylates PDH →  PDH →  acetyl CoA synthesis Low energy supply: ADP, pyruvate PDH phosphatase → dephosphorylation of PDH →  PDH →  acetyl CoA synthesis 20