Which enzyme converts pyruvic acid to lactic acid during anaerobic glycolysis?

• A. Pyruvate dehydrogenase
• B. Lactate dehydrogenase
• C. Alcohol dehydrogenase
• D. Lactate oxidase

Answer: (B)

Under anaerobic conditions, cells need to keep glycolysis going by regenerating NAD+. The way this happens is by converting pyruvate to lactate, using NADH and producing NAD+. The enzyme that does this exactly is lactate dehydrogenase, which transfers hydrogen from NADH to pyruvate to form lactate and NAD+.

Pyruvate dehydrogenase would push pyruvate into the aerobic pathway as acetyl-CoA, not into lactate. Alcohol dehydrogenase is involved in ethanol fermentation in microorganisms, not human anaerobic glycolysis. Lactate oxidase would oxidize lactate rather than generate it. So lactate dehydrogenase is the correct enzyme for converting pyruvic acid to lactic acid.