Question

When pyruvate is reduced by NADH to lactate, which hydrogen in lactate comes from NADH?

Short answer

When pyruvate is reduced to lactate, the alpha hydrogen in lactate comes from NADH.

Step-by-step solution

Lactate dehydrogenase

LDH is known as lactate dehydrogenase. It is the stereospecific enzyme used to interconvert lactate to pyruvate or pyruvate to lactate. It is also called anaerobic homolactic fermentation, in which nicotine amide adenine dinucleotide is used as the cofactor for reaction and acts as a hydrogen acceptor or donor.

Reduction of pyruvate to lactate

Conversion of pyruvate to lactate is a reduction that the ketonic group of the pyruvate is reduced to a hydroxyl group of lactate in the presence of NADH, and the hydrogen of the nicotine amide adenine dinucleotide is gained by lactate at its alpha position.