Unexpectedly enhanced stereoselectivity of peroxidase-catalyzed sulfoxidation in branched alcohols

Lyophilized horseradish peroxidase (HRP) exhibits poor stereoselectivity in the sulfoxidation of thioanisole when the enzyme is either redissolved in water orsuspendedinorganicsolvents.However,whenHRPis co-lyophilized in the presence of lyoprotectants or ligands, its stereoselectivity, although still low in most organic solvents, increases up to 4-fold if assayed in secondary or tertiary alcohols (but not in their linear isomers). A mechanistic hypothesisis presented explaining this puzzling phenomenon on the basis of a model of the active site of the enzyme-substrate complex derived from its X-ray crystal structure by means of molecular dynamics and energy minimization.