| Question |
Answer |
| Step 1 CAC |
Citrate synthase, oxalcetate (OAA) and acetyl CoA join by aldol condensation at OAA C2 (carbonyl group); subsequent cleavage of citryl CoA thioester bond drives reaction. citrate synthase reaction example of ordered substrate binding
|
| Step 2 CAC |
aconitase isomerizes citrate to isocitrate, the C-3 moves to C-2 position |
| Step 3 CAC |
isocitrate DH oxidatively decarboxylates isocitrate. two electrons removed to form NADH+ and H+, caboxyl leaves as CO2 |
| step 4 CAC |
a-ketoglutarate DH oxidatively decarboxylates a-KG. NADH+ and H+ is produced and a 4-C succinyl group is generated, reaction scheme is identical to pyruvate DH |
| step 5 CAC |
succinyl CoA synthetase produces succinate and GTP. a substrate level phosphorylation is coupled to cleavage if succinyl-CoA thioester bond. involves a phosphohistidine intermediate |
| step 6 CAC |
succinate is oxydized to fumarate by succinate dehydrogenase. electrons captured by FAD rather than NAD. enzyme is anchored to matrix face of inner mitochondrial membrane. part of electron transport system |
| Step 7 CAC |
Fumarase catalyzes the stereospecific hydration of the C2 and C3 double bond of Fumarate formung L-Malate |
| Step 8 CAC |
Malate DH oxidizes malate. NADH + H+ is produced and oxaloacetate is regenerated. energetically unfavorable under standard conditions, but occurs in vivo because of exergonic upstream and downstream rxns |
| symmetric molecules acted on asymmetrically |
citrate, aconitase moves OH specifically to C2, fumarate, fumarase adds water such that only L-malate is formed |
Ch.18 LTI-MA 509
