Lecture 10-15 - Lecture 10-15 THE CITRIC ACID CYCLE AT A...

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Lecture 10-15 THE CITRIC ACID CYCLE AT A GLANCE Reaction Enzyme Co-substrate Effectors G 0 0 pyruvate + CoA + NAD+ Ac-CoA + CO 2 + NADH pyruvate dehydrogenase complex * TPP, FAD, lipoic acid, CoA, NAD + 1 Ac-CoA + oxaloacetate citrate + CoASH citrate synthetase * CoA NADH,Succ-CoA (-) -32.2 2a citrate cis -aconitate aconitase Fe++ +6.3 2b cis -aconitate isocitrate aconitase Fe++ 3a isocitrate + NAD+ oxalosuccinate + NADH isocitrate dehydrogenase * NAD+ NADH (-) Ca++,ADP (+) -20.9 3b oxalosuccinate ⇔α- ketoglut + CO 2
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isocitrate dehydrogenase * Mn++ 4 α- ketoglut+ CoA + NAD+ Sc-CoA + CO 2 + NADH α -ketoglutarate dehydrogenase complex* TPP, FAD, lipoic acid, CoA, NAD+ NADH,, Sc-CoA(-) Ca++ (+) -33.5 5 Sc-CoA+ Pi + GDP succinate + CoA + GTP succinyl-CoA synthetase CoA -2.9 6 succinate + FAD fumarate + FADH 2 succinate dehydrogenase FAD, Fe++ 0 7 fumarate malate fumarase -3.8 8 malate + NAD+ oxaloacetate + NADH malate dehydrogenase NAD+ +29.7 net Ac-CoA + 3 NAD + + FAD +GDP + Pi + 2H 2 O 2CO 2 + CoA + 3NADH + FADH 2 + GTP -57.3 *sites of regulation
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Citric Acid Cycle or Krebs Cycle or Tricarboxylic Acid Cycle (TCA) next stop for pyruvate energy production intermediates in other pathways occurs in mitochondrial matrix ; one reaction occurs on the inner membrane oxidative decarboxylation--lose two carbons as CO2 KU Medicinal Biochemistry prepared by Dr. Allen Rawitch
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KU Medicinal Biochemistry prepared by Dr. Allen Rawitch Conversion of pyruvate to acetyl-CoA--reactions that you should LEARN!! catalyzed by enzyme complex, pyruvate dehydrogenase complex or PDC regulatory point controlled by effectors (AC-CoA and NADH inhibits) and by covalent modification (phos/dephos) in mammals in mammals the activation by kinases is highly regulated in response to diet and exercises; genetic defects in PDC subunits occur: clinically presenting with high lactic acid and often varying levels of neuropathy; most common defect in X-linked E1alpha subunit SUBUNITS OF PDC --cubic symmetry--type of molecular machine: efficient way to get substrates/enzyme close together Enzyme Activity Function catalytic co- substrate # subunits pyruvate decarboxylase-E1 decarboxylate pyruvate TPP 24 dimers dihydrolipoyl qtransacetylase-E2 transfer acetyl group to CoA lipoic acid, CoA 8 trimers forms core
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dihydrolipoyl dehydrogenase-E3 reoxidizes dihydrolipoamide NAD + , FAD 6 dimers Pyruvate dehydrogenase (E1)--animation of PDC reactions TPP (thiamine pyrophosphate)-2 heterocyclic rings o pyruvate is bound to TPP, release of CO2 Dihyrolipoyl transacetylase (E2*) transfer of acetyl group to lipoamide transfer acetyl group from lipoamide to CoA
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KU Medicinal Biochemistry prepared by Dr. Allen Rawitch lipoic acid covalently bound to dihydrolipoyl transacetlylase via lysine o active group called lipoamide o simultaneous oxidation and reduction of disulfide o serves as an electron carrier and acetyl group carrier
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Lecture 10-15 - Lecture 10-15 THE CITRIC ACID CYCLE AT A...

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