Stereoselective reduction of carbonyl compounds with Actinomycete: purification and characterization of three alpha-keto ester reductases from Streptomyces avermitilis.

We achieved the purification of three alpha-keto ester reductases (Streptomyces avermitilis keto ester reductase, SAKERs-I, -II, and -III) from Streptomyces avermitilis NBRC14893 whole cells. The molecular masses of the native SAKERs-I, -II, and -III were estimated to be 72, 38, and 36 kDa, respectively, by gel filtration chromatography. The subunit molecular masses of SAKERs-I, -II, and -III were also estimated to be 32, 32, and 34 kDa, respectively, by SDS-polyacrylamide gel electrophoresis. The purified SAKERs-II and -III showed a reducing activity for alpha-keto esters (in particular, for ethyl pyruvate). SAKER-I showed a high reducing activity not only toward the alpha- and beta-keto esters, but also toward alpha-keto acid. The N-terminal region amino acid sequences of SAKERs-I, -II, and -III were identical to that of a putative oxidoreductase, SAV2750, a putative oxidoreductase, SAV1849, and a putative oxidoreductase, SAV4117, respectively, hypothetical proteins coded on the S. avermitilis genome.