Some properties of mitochondrial and cell sap alanine aminotransferase of the rat heart.

Alanine aminotransferase activity is present in mitochondria and the cell sap fraction of the rat myocardium. As distinct from the cell sap form, mitochondrial alanine aminotransferase was significantly inhibited by chloride ions, maleate and incubation medium temperatures of over 40 degrees C. Activity of the cell sap enzyme was inhibited by phosphate and stimulated by temperatures of over 40 degrees C. The pH optimum for cell sap alanine aminotransferase was in the region of 8, while for the mitochondrial enzyme it had a wider range (pH 7.3-8.2). D,L-penicillamine, and antagonist of vitamin B6, inhibited alanine aminotransferase activity equally in intact and tritonized mitochondria and in the cell sap fraction. The activity of mitochondrial and cell sap alanine aminotransferease rose in correlation to the stage of ontogenesis, the maximum increase being observed in the cell sap fraction 14-20 days after birth. The addition of coenzyme to the incubation medium did not affect the activity of either mitochondrial or cell sap alanine aminotransferase. The results indicate that there are two different alanine aminotransferase enzymes in the rat heart, with different intracellular localizations and probably with different regulative functions.