If bionic pyruvate dehydrogenase activity resembles normal enzyme activity, the

Question

If bionic pyruvate dehydrogenase activity resembles normal enzyme activity, the architecture of bionic pyruvate dehyrogenase should consist of:

A. five distinct enzymes in a complex
B. three catalytic subunits and two regulatory subunits containing lipoic acid in a complex.

C. three subunits with distinct enzymatic activities, each of which has a covalently bound lipoic acid
D. two subunits with distinct specificities for catalyzing reactions involving pyruvate and/or acetyl-CoA and one subunit which does not catalyze any reaction directly involving pyruvate or acetyl-CoA.
E. three subunits assembled into a cylinder that bind pyruvate in a concerted fashion so that pyruvate enters at one end and acetyl-CoA emerges at the other end.

Explain why each answer is incorrect and I will rate you well

Explanation / Answer

Answer:

Correct option: D. two subunits with distinct specificities for catalyzing reactions involving pyruvate and/or acetyl-CoA and one subunit which does not catalyze any reaction directly involving pyruvate or acetyl-CoA.

Explanation:

Pyruvate dehydrogenase complex is an association of 3 enzymes that convert pyruvate into acetyl CoA.

The three subunits are -

1. Pyruvate dehydrogenase (E1) with cofactor TPP (Thiamine pyrophosphate). It catalyses the decarboxylation reaction involving the pyruvate.

2. Dihydrolipoyl transacetylase (E2) with 2 cofactors lipoate and coenzyme A. It catalyses the formation of acetyl CoA.

3. Dihydrolipoyl dehydrogenase (E3) with 2 cofactors FAD and NAD+. It is not involved directly in the main conversion reaction of pyruvate into acetyl CoA. E3 reduces NAD+ and reoxidises dihydrolipoamide.

Option A is incorrect as Pyruvate dehydrogenase complex is made up of three distinct enzymes rather than five.

Option B is incorrect as there are only three subunits - E1, E2 and E3 in the complex.

Option C is incorrect as only subunit E2 has a covalently bond lipoic acid.

Option E is incorrect as three subunits are not structurally associated in the form of cylinder. Each of them have different functions to perform (enzymatic activity). E1 interacts with pyruvate, while E2 is associated with generation of acetyl CoA. E3 reduces NAD+ and reoxidises dihydrolipoamide bringing back the normalcy.

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