Final answer:
Lactate dehydrogenase (LDH) is a protein that acts as an enzyme reducing pyruvic acid to lactate while also oxidizing NADH to NAD+, playing a key role in anaerobic glycolysis.
Step-by-step explanation:
Of the statements provided about lactate dehydrogenase (LDH), both (1) It is a protein, and (3) It reduces another molecule (pyruvic acid), are true. LDH is an enzyme that catalyzes the interconversion of lactate to pyruvate and vice versa. This reaction is a significant part of the anaerobic glycolysis pathway that occurs in virtually every cell of the body. The enzyme not only facilitates the reduction of pyruvate into lactate but also is involved in the oxidation of NADH to NAD+, which can then participate in further glycolytic reactions allowing additional glucose molecules to be oxidized.
In essence, during this process, pyruvate accepts the electrons from NADH, leading to the production of lactate and the regeneration of NAD+, crucial for maintaining the glycolytic cycle under anaerobic conditions. LDH is considered a reductase when it catalyzes the conversion of pyruvate to lactate and as a dehydrogenase when it helps in the oxidation of NADH.