4‐Aminobutyrate: 2‐oxoglutarate aminotransferase of Streptomyces griseus

• Published in: European journal of biochemistry Vol. 146; no. 1; pp. 101 - 106
• Main Authors: YONAHA, Kazuo, SUZUKI, Koji, TOYAMA, Seizen
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.01.1985
• ISSN: 0014-2956; 1432-1033
• DOI: 10.1111/j.1432-1033.1985.tb08625.x

4‐Aminobutyrate: 2‐oxoglutarate aminotransferase of Streptomyces griseus was purified to homogeneity on disc electrophoresis. The relative molecular mass of the enzyme was found to be 100000 ± 10000 by a gel filtration method. The enzyme consists of two subunits identical in molecular mass (Mr 50000 ± 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 104000, 11 400 and 7280 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°C. The enzyme is stable at pH 6.0–10.0 and at temperatures up to 50°C. Pyridoxal 5′‐phosphate protects the enzyme from thermal inactivation. The enzyme catalyzes the transamination of ω‐amino acids with 2‐oxoglutarate; 4‐aminobutyrate is the best amino donor. The Michaelis constants are 3.3 mM for 4‐aminobutyrate and 8.3 mM for 2‐oxoglutarate. Low activity was observed with β‐alanine. In addition to ω‐amino acids the enzyme catalyzes transaminiation with ornithine and lysine; in both cases the D isomer is preferred. Carbonyl reagents and sulfhydryl 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.