The purification and properties of L-histidine--2-oxoglutarate aminotransferase from Pseudomonas testosteroni

1. Inducible L-histidine--2-oxoglutarate aminotransferase was purified some 170-fold from extracts of Pseudomonas testosteroni. 2. The preparation showed only one major component after electrophoresis on polyacrylamide gels, though additional minor bands were observed when samples concentrated on a DEAE-cellulose column were used. 3. The molecular weight of the enzyme was found to be approx. 70000 by chromatography on Sephadex G-200. 4. The purification scheme produced enzyme that was inactive in the absence of pyridoxal 5'-phosphate. 5. The equilibrium constant for the reaction L-histidine+2-oxoglutarate equilibrium imidazolylpyruvate+L-glutamate was 0.49. 6. The reaction mechanism was Ping Pong. 7. The enzyme was shown to have only low activity towards aromatic amino acids and was highly specific for 2-oxoglutarate.