Alanine Aminotransferase

An examination of the subcellular distribution of alanine aminotransferase activity in pig cardiac tissue showed that about 10% of the total activity was bound to particulate material, with the highest specific activity in the sarcosomal fraction. The soluble enzyme was obtained in a high state of purity, as indicated by sedimentation velocity, starch gel electrophoresis, and spectral analyses. It had a sedimentation coefficient of 6.0 and an estimated molecular weight of about 100,000. Spectral, fluorescent, and optical rotatory properties of the enzyme are described. The enzyme-substrate interactions were studied by kinetic and spectral methods. Kinetic parameters of the enzymecatalyzed reaction involving amino transfer from L-alar&e to oc-ketoglutarate were determined at 37’, pH 7.8. At pH 6.9, pyruvate was found to bind effectively to the phosphopyridoxal form of the enzyme and, thereby, competitively inhibit amino transfer from both alanine and glutamate to pyruvate.