Purification and Characterization of an Enantioselective Amidase from Pseudomonas chlororaphis B23

An amidase produced by Pseudomonas chlororaphis B23 was purified and characterized. The purification procedure used included ammonium sulfate precipitation and hydrophobic, anion-exchange, gel filtration, and ceramic hydroxyapatite chromatography steps. This amidase has a native molecular mass of about 105 kDa and is a homodimer whose subunits have a molecular mass of 54 kDa. The enzyme exhibited maximal activity at 50(deg)C and at pH values ranging from 7.0 to 8.6. We found no evidence that metal ions were required, and the enzyme was inhibited by several thiol reagents. This amidase exhibited activity against a broad range of aliphatic and aromatic amides and exhibited enantioselectivity for several aromatic amides, including 2-phenylpropionamide (enantiomeric excess [ee] = 100%), phenylalaninamide (ee = 55%), and 2-(4-chlorophenyl)-3-methylbutyramide (ee = 96%), but not 2-(6-methoxy-2-naphthyl)propionamide (the amide form of naproxen) (ee = 0%). The characteristics of the P. chlororaphis B23 amidase are the same as the characteristics of enantioselective amidases described by Mayaux et al. (J. F. Mayaux, E. Cerbelaud, F. Soubrier, D. Faucher, and D. Petre, J. Bacteriol. 172:6764-6773, 1990; J. F. Mayaux, E. Cerbelaud, F. Soubrier, P. Yeh, F. Blanche, and D. Petre, J. Bacteriol. 173:6694-6704, 1991) and Kobayashi et al. (M. Kobayashi, H. Komeda, T. Nagasawa, M. Nishiyama, S. Horinouchi, T. Beppu, H. Yamada, and S. Shimizu, Eur. J. Biochem. 217:327-336, 1993).