Question

In which of the following reactions, reduction of NAD does not occur?

• A. Isocitric acid → α-ketoglutaric acid
• B. Malic acid → Oxaloacetic acid
• C. Pyruvic acid → Acetyl coenzyme
• D. Succinic acid → Fumaric acid

Answer 1

The correct option is D Succinic acid → Fumaric acid

During the Krebs cycle, the conversion of isocitric acid to α-ketoglutaric acid involves the reduction of NAD with an intermediate of oxalosuccinic acid by 2 steps- oxidation and decarboxylation.

Malic acid undergoes oxidation to form oxaloacetic acid where NAD is reduced to $NAD{H}_2$.

Pyruvic acid undergoes oxidation and decarboxylation to form acetyl coenzyme A where NAD acts as a reducing agent.

Succinic acid undergoes oxidation to form fumaric acid, where FAD undergoes reduction to $FAD{H}_2$. There is no involvement of NAD in this reaction.