The enantioselectivity of quinohaemoprotein alcohol dehydrogenases: mechanistic and structural aspects

Quinohaemoprotein alcohol dehydrogenases, QH-ADHs, isolated from Acetobacter, Gluconobacter and Comamonas species show appreciable enantioselectivity in the oxidation of chiral primary and secondary alcohols. Current views of the structural and mechanistic factors of importance for the understanding of the enantioselective performance of these enzymes are reviewed. Structural properties of QH-ADH, Type I, from C. testosteroni, and QH-ADH, Type II, from A. pasteurianus have been deduced from homology modeling studies based on the X-ray crystallographic data available for PQQ-containing quinoprotein methanol dehydrogenases, MDHs. Mechanisms that have been proposed for quino(haemo)protein alcohol dehydrogenase-catalyzed substrate oxidation are discussed in relation to the constraints set by the observed enantioselectivity.