Activity and expression of aspartate aminotransferase during the reproductive cycle of a fresh water fish, Clarias batrachus

Aspartate amino transferase (AspT; EC: 2.6.1.1) is one of the key enzyme of aspartate malate shuttle and non-essential amino acid metabolism. In order to clarify the change of the activities of both cytosolic (c-) and mitocho ndrial (m-) AspT isoenzymes during the different reproductive stages of Cla rias batrachus, an air-breathing carnivorous freshwater fish, the c- and m- AspT activities were measured spectrophotometrically in liver, heart, kidn ey, brain and ovary during the pre-spawning, spawning and post-spawning pha ses of the annual reproductive cycle of this fish. Maximum activities were observed during the spawning phase, followed by pre- and postspawning phase s. The native agarose gel electrophoretic pattern revealed two AspT forms, c-AspT and m-AspT, throughout the pre- to post-spawning phases. However, th e spawning phase was marked by the expression of an additional anionic form of c-AspT in all tissues studied. These results indicate a distinct utiliz ation of aspartate particularly in the spawning phase in fish in the centra l metabolic path via transamination reactions, and suggest a control of the enzyme activity by the expression of the additional c-AspT gene, especiall y at the spawning phase.