Affinity labeling of aspartate aminotransferase isozymes by bromopyruvate.

Incubation with bromopyruvate did not cause appreciable inactivation of either supernatant or mitochondrial isozyme of aspartate aminotransferase from pig heart. In the presence of either L-cysteine sulfinate or L-aspartate, however, bromopyruvate rapidly inactivated both isozymes. Bromopyruvate also acted as a keto acid substrate in the conversion of the pyridoxamine form of both enzymes to their pyridoxal forms. This fbrding, together with the demonstration of the equimolar formation of oxalacetate, pyruvate, and ammonia from L-aspartate and bromopyruvate, supported the following reaction sequences: