The TCA Cycle The TCA Cycle A common metabolic pathway for glucose, aa and fatty acid • Citric Acid Cycle, Krebs Cycle • Pyruvate (actually acetate) fro m glycolysis is degraded to CO 2 • Some ATP is produced • More NADH is made • NADH goes on to make more ATP i n electron transport and oxidat ive phosphorylation
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The TCA Cycle The TCA Cycle A common metabolic pathway for glucose, aa and fatty acid Citric Acid Cycle, Krebs Cycle Pyruvate (actually acetate) from glycolysis.
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The TCA CycleThe TCA CycleA common metabolic pathway for glucose, aa and fatty acid
• Citric Acid Cycle, Krebs Cycle
• Pyruvate (actually acetate) from glycolysis is degraded to CO2
• Some ATP is produced
• More NADH is made
• NADH goes on to make more ATP in electron transport and oxidative phosphorylation
Entry into the TCA Cycle
• Pyruvate Dehydrogenase Complex
•
☻Pyruvate is oxidatively decarboxylated to form acetyl-CoA
☻Pyruvate dehydrogenase uses TPP, CoASH, lipoic acid, FAD and NAD+
☻Pyruvate dehydrogenase (E1) (丙酮酸脱氢酶 )
☻Dihydrolipoyl transacetylase (E2) (二氢硫辛酰转乙酰基酶 )
☻Dihydrolipoyl dehydrogenase (E3) (二氢硫辛酰脱氢酶 )
Pyruvate Acetyl-CoA Pyruvate Dehydrogenase
Complex
Pyruvate dehydrogenase complex consists of three enzymes
Arsenic Compounds Are Poisonous in part because They Sequester Lipoamide
① Condensation
Citrate SynthaseCitrate Synthase• Formation of citrate
☻Another example for the induced fit model
☻OAA, the first substrate to bind to the enzyme, induce a large conformational change, creating a binding site for the second substrate, acetyl-CoA. When citroyl-CoA forms on the enzyme surface, another conformational change brings the side of a crucial Asp residue into position to cleavage the thioester.
☻This mechanism decreases the likelihood of premature and unproductive cleavage of the thioester bond of acetyl-CoA
AconitaseAconitase• Isomerization of Citrate to Isocitrate
☻Citrate is a poor substrate for oxidation
☻So aconitase isomerizes citrate to yield isocitrate which has a secondary -OH, which can be oxidized
☻Note the stereochemistry of the Rxn: aconitase removes the pro-R H of the pro-R arm of citrate!
☻Aconitase uses an iron-sulfur cluster
② Dehydration and hygration
Isocitrate DehydrogenaseIsocitrate Dehydrogenase• Oxidative decarboxylation of isocitrate to y
ield -ketoglutarate
☻Classic NAD+ chemistry (hydride removal) followed by a decarboxylation
☻Isocitrate dehydrogenase is a link to the electron transport pathway because it makes NADH