Characterization of the enantioselective properties of the quinohemoprotein alcohol dehydrogenase of Acetobacter pasteurianus LMG 1635. 1. Different enantiomeric ratios of whole cells and purified enzyme in the kinetic resolution of racemic glycidol

Resting cells of Acetobacter pasteurianus LMG 1635 (ATCC 12874) show apprec iable enantioselectivity (E=16-18) in the oxidative kinetic resolution of r acemic 2,3-epoxy-1-propanol, glycidol. Distinctly lower values (E=7-9) are observed for the ferricyanide-coupled oxidation of glycidol by the isolated quinohemoprotein alcohol dehydrogenase, QH-ADH, which is responsible for t he enantiospecific oxidation step in whole cells. The accuracy of E-values from conversion experiments could be verified using complementary methods f or the measurement of enantiomeric ratios. Effects of pH, detergent, the us e of artificial electron accepters, and the presence of intermediate aldehy des, could be accounted for. Measurements of E-values at successive stages of the purification showed that the drop in enantioselectivity correlates w ith the separation of QH-ADH from the cytoplasmic membrane. It is argued th at the native arrangement of QH-ADH in the membrane-associated complex favo rs the higher E-values. The consequences of these findings for the use of w hole cells versus purified enzymes in biocatalytic kinetic resolutions of c hiral alcohols are discussed.