The ester-hydrolyzing enzyme families, including lipase and esterase, mediated a broad range of reactions and, thus, were able to act on a variety of ester compounds that are found naturally or exploited industrially. With the increasing demand for pharmacological use, attempts to produce an enantionter (S)-ketoprofen from the corresponding ethyl ester have recently been proliferating, but information about the structure and function of related enzymes has not been reported to date in detail. Here, we reported the construction, expression, and one-step purification of a potential esterase in Escherichia coli with a hexahistidine tag at its N-terminus. The expression level of the enzyme was more than 20% of the total protein in E. Coli, resulting in approximately 1.2 mg of the purified proteins by an affinity resin, Ni-NTA, from a 0.2 L of bacterial culture in a single step. As typical properties, its innate traits that revealed favorable reactions at alkaline pH and high activity to the triglycerides composed of short chain fatty acids (< C-6) supported the enzyme to be an esterase. The enzyme was determined to be a monomer with a calculated molecular mass of 42 kDa and showed quite a high activity to rac-ketoprofen ethyl ester (27,000 U), with strict selectivity to (S)-enantiomer (>99% ee(p)). The small-scale conversion using the recombinant enzyme strongly suggested the enzyme to be useful for enzyme-mediated chiral resolution of (S)-ketoprofen. (C) 2003 Elsevier Science (USA). All rights reserved.