20 - Citric Acid Cycle, Part 2

20 - Citric Acid Cycle, Part 2 - Citric Acid Cycle. Part II...

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Citric Acid Cycle Part I Citric Acid Cycle. Part II Learning Objective • Eight reactions and eight enzymes of the citric acid cycle Learning Objectives Regulation of the citric acid cycle •ATP energy equivalent released in glucose catabolism • Regulation of the citric acid cycle • Metabolic reactions related to the citric acid cycle
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1. Citrate Synthase • Catalyzes the condensation of Acetyl- C A d l t t CoA and oxaloacetate • The initial reaction of the citric acid cycle • Carbon atoms from carbohydrates, fatty acids, and amino acids enter the cycle in COO - COO - H 2 O the form of acetyl group attached to CoA. C=O CH 2 HO-C-COO - CH 2 CH 2 + CH 3 -C(O)-S-CoA HS-CoA COO - COO - Oxaloacetate Citrate Acetyl-CoA ! G 0' " -32 kJ/mol
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2. Aconitase • Aconitase catalyzes the reversible isomerization of citrate and isocitrate isomerization of citrate and isocitrate, with cis -aconitate as an intermediate. The hydration of the double bond of • The hydration of the double bond of cis-aconitate could yield four stereoisomers. The enzyme catalyzes COO - CH H 2 O COO - CH COO - CH H 2 O synthesis of only one isomer, isocitrate. HO-C-COO - 2 CH 2 C-COO - 2 CH H-C-COO - 2 HO-C-H COO - Citrate COO - COO - cis -Aconitate Isocitrate
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3. NAD + -Dependent Isocitrate Dehydrogenas • The enzyme catalyzes the oxidative decarboxylation of isocitrate to # Isocitrate Dehydrogenase decarboxylation of isocitrate to - ketoglutarate. The reaction produces CO 2 and NADH. • The CO 2 carbon entered the first stage of the citric acid cycle as a component of oxaloacetate rather than COO - COO - COO - NADH COO -
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20 - Citric Acid Cycle, Part 2 - Citric Acid Cycle. Part II...

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