n. any of a class of transferase enzymes that catalyze the transfer of an amino group (–NH2) from a donor molecule to a recipient molecule. Two of the better known aminotransferases are aspartate aminotransferase and alanine aminotransferase, which are normally found in the liver and heart, respectively, and are released into the bloodstream as a result of damage to those organs. Hence, they are used as indicators in liver and heart function tests.