4‐Aminobutyrate: 2‐oxoglutarate aminotransferase of Streptomyces griseus:

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Abstract
4-Aminobutyrate:2-oxoglutarate aminotransferase of Streptomyces griseus was purified to homogeneity on disc electrophoresis. The relative molecular mass (Mr) of the enzyme was found to be 100,000 .+-. 10,000 by a gel filtration. The enzyme consists of 2 subunits identical in molecular mass (Mr 50,000 .+-. 1000). The transaminase is composed of 486 amino acids/subunit containing 10 and 12 residues of half-cystine and methionine, respectively. The NH2-terminal amino acid sequence of the enzyme was determined to be Thr-Ala-Phe-Pro-Gln. The enzyme exhibits absorption maxima at 278 nm, 340 nm and 415 nm with a molar absorption coefficient of 104,000, 11,400 and 7820 M-1 cm-1, respectively. The pyridoxal 5''-phosphate content was calculated to be 2 mol/mol enzyme. The enzyme has a maximum activity in the pH range of 7.5-8.5 and at 50.degree. C. The enzyme is stable at pH 6.0-10.0 and at temperatures up to 50.degree. C. Pyridoxal 5''-phosphate protects the enzyme from thermal inactivation. The enzyme catalyzes the transamination of .omega.-enzyme acids with 2-oxoglutarate: 4-aminobutyrate is the best amino donor. The Km 3.3 mM for 4-aminobutyrate and 8.3 mM for 2-oxoglutarate. Low activity was observed with .beta.-alanine. In addition to .omega.-amino acids the enzyme catalyzes transamination with ornithine and lysine; in both cases the D isomer is preferred. Carbonyl reagents and SH reagents inhibit the enzyme activity. Chelating agents, non-substrate L and D-2-amino acids, and metal ions except cupric ion showed no effect on the enzyme activity.