Slide 1Figure 21-1 Reactions of the citric acid cycle.Slide 3Figure 21-3 Electron micrographs of the E. coli pyruvate dehydrogenase multienzyme complex. (a) The intact complex. (b) The dihydrolipoyl transacetylase (E2) “core” complex.Figure 21-4 Structural organization of the E. coli PDC.Table 21-1 The Coenzymes and Prosthetic Groups of Pyruvate Dehydrogenase.Figure 21-6 The five reactions of the PDC.Figure 21-7 Interconversion of lipoamide and dihydrolipoamide.Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Figure 21-8 Domain structure of the dihydrolipoyl transacetylase (E2) subunit of the PDC.Figure 21-11 Electron microscopy–based images of the bovine kidney pyruvate dehydrogenase complex at ~35 Å resolution. (a) The entire particle as viewed along its 3-fold axis of symmetry. (b) A cutaway diagram. (c) A cutaway diagram as in Part b but with E3 dimers (Fig. 21-13a) shown at 20 Å resolution (red) modeled into the pentagonal openings of the E2 coreSlide 18Figure 21-12a X-Ray structure of E1 from P. putida branched-chain a-keto acid dehydrogenase. (a) The a2b2 heterotetrameric protein.Figure 21-12b X-Ray structure of E1 from P. putida branched-chain a-keto acid dehydrogenase. (b) A surface diagram of the active site region.Slide 21Figure 21-14Catalytic reaction cycle of dihydrolipoyl DH.Figure 21-16 The reaction transferring an electron pair from dihydrolipoyl dehydrogenase’s redox-active disulfide in its reduced form to the enzyme’s bound flavin ring.Figure 21-17a Factors controlling the activity of the PDC. (a) Product inhibition.Figure 21-17 Factors controlling the activity of the PDC. (b) Covalent modification in the eukaryotic complex.Slide 26Figure 21-18a Conformational changes in citrate synthase. (a) Space-filling drawing showing citrate synthase in the open conformation. (b) Space-filling drawing showing citrate synthase in the closed, substrate-binding conformationFigure 21-19 Mechanism and stereochemistry of the citrate synthase reaction.Figure 21-20 Mechanism and stereochemistry of the aconitase reaction.Figure 21-21 Probable reaction mechanism of isocitrate dehydrogenase.Figure 21-22a Reactions catalyzed by succinyl-CoA synthetase. Formation of succinyl phosphate, a “high-energy” mixed anhydride.Figure 21-22b Reactions catalyzed by succinyl-CoA synthetase. Formation of phosphoryl–His, a “high-energy” intermediate.Figure 21-22c Reactions catalyzed by succinyl-CoA synthetase. Transfer of the phosphoryl group to GDP, forming GTP.Slide 34Figure 21-23 Covalent attachment of FAD to a His residue of succinate dehydrogenase.Slide 36Slide 37Slide 38Slide 39Table 21-2 Standard Free Energy Changes (DG°¢) and Physiological Free Energy Changes (DG) of Citric Acid Cycle Reactions.Figure 21-25 Regulation of the citric acid cycle.Slide 42Suggested problems Ch 18: 3, 4, 5, 7, 8, 9Ch 19: read pp. 657-660, 673-683, 707-714, 718-9read to overview pp. 683 through 690skim the rest.Problems: 2, 6, 10Suggested Problems Ch 20: 1, 4, 6, 7, 8, 9, 13Suggested Problems Ch 21: 1, 2, 3, 4, 6, 8, 9, 10, 12, 13, 14Figure 21-1 Reactions of the citric acid cycle. Page 766Page 768Figure 21-2 Chemical structure of acetyl-CoA.Figure 21-3 Electron micrographs of the E. coli pyruvate dehydrogenase multienzyme complex. (a) The intact complex. (b) The dihydrolipoyl transacetylase (E2) “core” complex. Page 769Figure 21-4Structural organization of the E. coli PDC.Page 769E2 Dihydrolypoly transacetlyase corePDH: 24 Subunits (E1)24 subunits12 dihydrolypoyl dehydrogenase (E3)a+bTable 21-1 The Coenzymes and Prosthetic Groups of Pyruvate Dehydrogenase.Page 771Figure 21-6The five reactions of the PDC. Page 770Nucleophile and electron sinkFigure 21-7 Interconversion of lipoamide and dihydrolipoamide.Page 771Figure 21-8 Domain structure of the dihydrolipoyl transacetylase (E2) subunit of the PDC.Figure 21-11 Electron microscopy–based images of the bovine kidney pyruvate dehydrogenase complex at ~35 Å resolution. (a) The entire particle as viewed along its 3-fold axis of symmetry. (b) A cutaway diagram. (c) A cutaway diagram as in Part b but with E3 dimers (Fig. 21-13a) shown at 20 Å resolution (red) modeled into the pentagonal openings of the E2 core Page 774Figure 21-12a X-Ray structure of E1 from P. putida branched-chain a-keto acid dehydrogenase. (a) The a2b2 heterotetrameric protein. Page 776Figure 21-12b X-Ray structure of E1 from P. putida branched-chain a-keto acid dehydrogenase. (b) A surface diagram of the active site region.Page 776What’s glutathione????????Figure 21-14Catalytic reaction cycle of dihydrolipoyl DH. Page 778Figure 21-16The reaction transferring an electron pair from dihydrolipoyl dehydrogenase’s redox-active disulfide in its reduced form to the enzyme’s bound flavin ring. Page 780Figure 21-17a Factors controlling the activity of the PDC. (a) Product inhibition.Page 781Figure 21-17 Factors controlling the activity of the PDC.(b) Covalent modification in the eukaryotic complex.Page 781Figure 21-1 Reactions of the citric acid cycle. Page 766Figure 21-18a Conformational changes in citrate synthase. (a) Space-filling drawing showing citrate synthase in the open conformation. (b) Space-filling drawing showing citrate synthase in the closed, substrate-binding conformationPage 782Figure 21-19 Mechanism and stereochemistry of the citrate synthase reaction.Page 783Figure 21-20 Mechanism and stereochemistry of the aconitase reaction.Page 784Figure 21-21 Probable reaction mechanism of isocitrate dehydrogenase.Page 785Figure 21-22a Reactions catalyzed by succinyl-CoA synthetase. Formation of succinyl phosphate, a “high-energy” mixed anhydride. Page 787succinateFigure 21-22b Reactions catalyzed by succinyl-CoA synthetase. Formation of phosphoryl–His, a “high-energy” intermediate.Page 787Figure 21-22c Reactions catalyzed by succinyl-CoA synthetase. Transfer of the phosphoryl group to GDP, forming GTP.Page 787Succinate  Fumarate+ FAD + FADH2Enzyme?OO-HHOO__Inhibited byMalonateFigure 21-23 Covalent attachment of FAD to a His residue of succinate dehydrogenase.Page 787Page 788Figure 21-24 Possible mechanisms for the hydration of fumarate as catalyzed by fumarase.Isotopic TestsCOO-CH3-+CoASH CH3C=OCoASHWhen in the TCA cycle would this label be lost as CO2?Table 21-2 Standard Free Energy Changes (DG°¢) and Physiological Free Energy Changes (DG) of Citric Acid Cycle Reactions.Page 790Figure 21-25Regulation of the citric acid cycle.Page