Which vitamin is a cofactor for the enzyme pyruvate dehydrogenase, linking glycolysis to the citric acid cycle?

Which vitamin is a cofactor for the enzyme pyruvate dehydrogenase, linking glycolysis to the citric acid cycle?

• A. Niacin
• B. Riboflavin
• C. Pantothenic acid
• D. Thiamin

Answer: (D)

Thiamin, in its active form thiamine pyrophosphate, acts as a cofactor for the pyruvate dehydrogenase complex, specifically enabling the E1 decarboxylase step that converts pyruvate into acetyl-CoA. This reaction is the essential bridge between glycolysis and the citric acid cycle, directing the end product of glycolysis into the TCA cycle for further energy harvest. Without adequate thiamin, this step slows, impairing acetyl-CoA production and glucose oxidation. Other vitamins also participate in the PDH complex (riboflavin for FAD, niacin for NAD+, pantothenic acid for CoA), but the question highlights thiamin as the critical cofactor for this linking step.

Thiamin, in its active form thiamine pyrophosphate, acts as a cofactor for the pyruvate dehydrogenase complex, specifically enabling the E1 decarboxylase step that converts pyruvate into acetyl-CoA. This reaction is the essential bridge between glycolysis and the citric acid cycle, directing the end product of glycolysis into the TCA cycle for further energy harvest. Without adequate thiamin, this step slows, impairing acetyl-CoA production and glucose oxidation. Other vitamins also participate in the PDH complex (riboflavin for FAD, niacin for NAD+, pantothenic acid for CoA), but the question highlights thiamin as the critical cofactor for this linking step.