Purification and characterization of a nicotinamide adenine dinucleotide-dependent secondary alcohol dehydrogenase from Candida boidinii

From the yest Candida biodinili grown on glucose a new secondary alcohol dehydrogenase was purified 426-fold by heat treatment, column chromatography on DEAE-Sephacel, affinity chromatography on Blue Sepharose Cl-6b, and gel filtration on Sephacryl S-300. The purified enzyme was homogeneous as judged by analytical polyacrylamide gel electrophoresis. The molecular weight was found to be 150 000 by sedimentation equilibirum as well as by flitration. The enzyme appears to be composed of four identical subunits (M_r = 38000) as determined by SDS-gel electrophoresis. The enzyme catalyzes the oxidation of isopropanol to acetone in the presence of NAD⁺ as an electron acceptor. The K_m values were found to be 0.099 mM for isopropanoi and 0.14 mM for NDA⁺. Besides isopropanol also other secondary alcohols like butan-2-ol, pentan-2-ol, pentan-3-ol, hexan-2-ol, cyclobutanol, cyclopentanol, and cyclohexanol served as a substrate and were oxidazed to the correponding ketones. Isopropanol seems to be the best substrate for this enzyme which we therefore call isopropanol dehydrogenase. Primary alcohols are not oxidized by the enzyme. The optimum pH for enzymatic activity in the oxidation reaction was found to be 9.0, the optimal temperature is 45°C. The isolectric point of the isopropanol dehydrogenase was found to be pH 4.9. The enzyme is inactivated by mercaptide-forming reagents and chelating agents, 2-mercaptoethanol is an inhibitor. Zinc ions appear necessary for enzyme productuion.