Question

1. The pyruvate dehydrogenase complex converts pyruvate to acetyl-CoA. What are the steps that pyruvate undergoes? Which coenzymes are involved in each step?

2. Mitochondrial extracts from pigeon breast muscle were incubated with

Experiment 1: Amytal, an inhibitor of complex I

Experiment 2: Malonate, a competitive inhibitor of succinate dehydrogenase

Which experiment will yield more ATP when the cycle is primed with intermediates?

Answer 1

1. The oxidative decarboxylation of pyruvate, leading to the formation acetyl-CoA, CO2 and NADH . This reaction is catalyzed by the enzyme Pyruvate Dehydrogenase. The coenzymes involved are; Thiamine pyrophosphate and lipoamide.The steps are:

Step A: With the help of TPP Pyruvate is decarboxylated by pyruvate dehydrogenase

Step B: The carbon of TPP; between the N and the S is oxidized and transferred as the acetyl group to lipoamide forming hydroxyethyl-TPP. CO2 is given off.

StepC: E2 (dihydrolipoyltransacetylase) oxidizes hydroxyethyl- to acetyl- and then transfers acetyl- to CoA, forming acetyl-CoA.

Step E: NAD+ is reduced to NADH.

1. Experiment 1 will yield more energy as the ATP synthesis, in this case, is blocked at the level of electron transport chain and not the Krebs cycle, so substrate level phosphorylation can occur.