Entropic and enthalpic contributions to the enantioselectivity of quinohaemoprotein alcohol dehydrogenases from Acetobacter pasteurianus and Comamonas testosteroni in the oxidation of primary and secondary alcohols

Quinohaemoprotein alcohol dehydrogenases, QH-ADHs, show appreciable enantio selectivity in the oxidation of certain chiral primary and secondary alcoho ls. We determined the effect of temperature on the enantiomeric ratio of st ructurally related enzymes, QH-ADH, Type I. from Comamonas testosteroni and QH-ADH, Type II, from Acetobacter pasteurianus. in the kinetic resolution of racemic 2,2-dimethyl-4-(hydroxymethyl)-1,3-dioxolane (solketal) and 2-bu tanol, respectively. It appears that entropic contributions to the stabiliz ation of the enantioselectivity-determining transition state play an import ant role in the enantiopreference. Consequences of these findings for the f ormulation of models that can be used to summarise the observed enantiosele ctivities are discussed.