Transaminase of Branched Chain Amino Acids

VI. Purification and Properties of the Hog Brain Enzyme

Abstract

Branched chain amino acid (valine, leucine and isoleucine)-α-ketoglutarate trans-aminase [EC 2. 6. 1. 6] was purified from hog brain supernatant by DEAE-cellulose, hydroxylapatite and DEAE-Sephadex column chromatographies. The purified enzyme was shown to be a single protein by ultracentrifugation, immuno-double diffusion and agar and acryamide gel electrophoreses. Its s_{20, W} was 3.3. Substrate specificity was limited to the substrates described above. The K_m values for the substrates and cofactor were (in mM): 0.56 for leucine, 0.67 for isoleucine, 1.4 for valine, 0.57 for a-ketogluta-rate and 0.0065 for pyridoxal phosphate. 2-Mercaptoethanol activated the enzyme. These properties, except the chromatographic behavior and molecular weight, are very similar to those of the enzyme in hog heart.
Anti-serum against hog brain enzyme inhibited the activity of the homologous enzyme and that of heart enzyme to a lesser extent. Conversely, anti-serum against hog heart enzyme neutralized the activities of both the heart and brain enzymes, though the inhibition of the latter was less. The properties of the two enzymes and their distributions in various hog tissues were compared.