Which enzyme catalyzes the reaction: lactase + NAD → pyruvate + NADH?

The enzyme that catalyzes the reaction of lactate and NAD to produce pyruvate and NADH is lactate dehydrogenase. This particular enzyme plays a crucial role in anaerobic respiration and the process of converting lactate, which is a product of glycolysis, back into pyruvate. The reaction involves the oxidation of lactate while simultaneously reducing NAD+ to NADH, which is essential for maintaining the redox balance within the cell during periods of low oxygen availability.

Lactate dehydrogenase can be found in various tissues, particularly in muscle cells, where it functions to help regenerate NAD+, allowing glycolysis to continue at a higher rate under anaerobic conditions. The generation of NADH in this reaction is also significant, as it can enter the electron transport chain during aerobic respiration when oxygen becomes available.

The other enzymes listed in the options have distinct functions and substrate specificities that do not encompass the conversion of lactate to pyruvate. Therefore, understanding the specific role of lactate dehydrogenase in this metabolic pathway helps clarify why it is the correct answer to the question posed.