Purification and characterization of a novel (S)-enantioselective transaminase from Pseudomonas fluorescens KNK08-18 for the synthesis of optically active amines

Pseudomonas fluorescens KNK08-18, showing (S)-selective transaminase activity, was isolated from soil by an enrichment culture method using (S)-7-methoxy-2-aminotetraline as the main nitrogen source. A transaminase was purified from the strain to homogeneity in seven steps. The relative mass of the enzyme was estimated to be 53 kDa on SDS-polyacrylamide gel electrophoresis and 120 kDa by gel filtration, suggesting a homodimeric structure. The optimal pH and temperature for enzyme activity were about 8.0-8.5 and 40 °C. The purified enzyme produced (S)-7-methoxy-2-aminotetraline, (S)-SMA, from 7-methoxy-2-tetralone (SMT) with high enantioselectivity. Although (S)-1-phenylethylamine was the best amino donor, β-alanine and 4-aminobutyric acid, which are good substrates for typical ω-amino acid transaminase (EC 2.6.1.18) and GABA transaminase (2.6.1.19), were not reacted. It aminated a broad range of carbonyl compounds containing aromatic, non-aromatic, and acidic and non-acidic substrates.