STUDIES OF THE REDUCTIVE BIOTRANSFORMATION OF SELECTED CARBONYL-COMPOUNDS BY WHOLE CELLS AND EXTRACTS OF BAKERS-YEAST, SACCHAROMYCES-CEREVISIAE

The progress of reductive biotransformations of a variety of earbonyl compounds by whole cells of baker's yeast was monitored with time. Biotransformation rates ranged from 0.11 to 112.12 mg product formed per g dry yeast per h. While rapid biotransformations of citronellal and ethyl benzoylformate were observed, complete conversion of substrate to product did not occur. Reductive conversions of ethyl- and methyl-acetoacetate went to completion in 6 and 12 h respectively. Ethyl mandelate was produced stereoselectively, favoring the (R)- stereoisomer and ethyl- and methyl-3-hydroxybutyrate were produced with (S)-enantiospecificity. Yeast crude extract and resuspended pellet fractions converted citronellal to citronellol in the presence of NAD(P)H. Ethyl benzoylformate and methyl- and ethyl-acetoacetate were preferentially reduced by yeast crude extract as compared to resuspended pellet and, in the case of the former two substrates, the reaction manifested a preference for NADPH over NADH.