Purification and characterization of rat liver mitochondrial phenylalanine pyruvate aminotransferase.

Phenylalanine pyruvate aminotransferase in rat liver was found in both the mitochondrial and supernatant fractions. Phenylalanine pyruvate aminotransferase was purified from rat liver mitochondria. The purified enzyme was specific for pyruvate, exhibiting no activity with 2-oxoglutarate as aminoacceptor, and utilized a wide range of amino acids as amino donors. Amino acids were effective in the following order of activity: L-phenylalanine > L-tyrosine > L-histidine > 3,4-dihydroxy-DL-phenylalanine. Very little activity was observed with L-tryptophan and 5-hydroxy-L-tryptophan. The apparent Km values for L-phenylalanine and L-histidine were 2.6 mM and 2.7 mM, respectively. The Km values for pyruvate were 5.0 mM and 1.5 mM with phenylalanine and histidine as amino donors, respectively. The pH optimum was near 9.0. Sucrose density gradient centrifugation gave a molecular weight of approximately 68,000. On the basis of subcellular distributions, substrate specificities, substrate inhibition, pH optima, polyacrylamide gel electrophoresis and some other properties, it was suggested that mitochondrial phenylalanine pyruvate aminotransferase was identical with mitochondrial histidine pyruvate aminotransferase.