Activity of Yeast Alcohol Dehydrogenases on Benzyl Alcohols and Benzaldehydes Characterization of Adh1 from Saccharomyces Carlsbergensis and Transition State Analysis

The substrate specificities of yeast alcohol dehydrogenases I and II from Saccharomyces cerevisiae (SceADH1 and SceADH2) and Saccharomyces carlsbergensis (ScbADH1) were studied. For this work, the gene for the S. carlsbergensis ADH1 was cloned, sequenced and expressed. The amino acid sequence of ScbADH1 differs at four positions as compared to SceADH1, including substitutions of two glutamine residues with glutamic acid residues, and has the same sequence as the commercial yeast enzyme, which apparently is prepared from S. carlsbergensis. The electrophoretic mobilities of ScbADH1, SceADH2 and commercial ADH are similar. The kinetics and specificities of ScbADH1 and SceADH1 acting on branched, long-chain and benzyl alcohols are very similar, but the catalytic efficiency of SceADH2 is about 10-100-fold higher on these substrates. A three-dimensional structure of SceADH1 shows that the substrate binding pocket has Met-270, whereas SceADH2 has Leu-270, which allows larger substrates to bind. The reduction of a series of p-substituted benzaldehydes catalyzed by SceADH2 is significantly enhanced by electron-withdrawing groups, whereas the oxidation of p-substituted aromatic alcohols may be only slightly affected by the substituents. The substituent effects on catalysis generally reflect the effects on the equilibrium constant for the reaction, where electron-withdrawing substituents favor alcohol. The results are consistent with a transition state that is electronically similar to the alcohol, supporting previous results obtained with commercial yeast ADH.