What reaction does Alanine Aminotransferase (ALT) catalyze?

Alanine Aminotransferase (ALT) is an enzyme that plays a crucial role in amino acid metabolism, specifically in the transamination process. The reaction catalyzed by ALT involves the conversion of pyruvate and glutamate into alanine and alpha-ketoglutarate. This transamination reaction is essential in the synthesis of alanine, which can be used in gluconeogenesis, especially during periods of fasting or intense exercise.

The significance of this reaction lies in the transfer of an amino group from glutamate to pyruvate, resulting in the formation of alanine and regenerating alpha-ketoglutarate. This mechanism not only serves to form essential metabolites but also helps in maintaining the nitrogen balance within the body.

In contrast, the other options involve different substrates or products that are not consistent with the function of ALT. For example, reactions involving aspartate or oxaloacetate in the context described do not involve the primary action of ALT, which specifically focuses on the interplay between pyruvate and glutamate. Thus, the reaction B accurately reflects the substrate specificity and the biological role of Alanine Aminotransferase.