title: A critical test of the "tunneling and coupled motion" concept in enzymatic alcohol oxidation.
abstract: The physical mechanism of C-H bond activation by enzymes is the subject of intense study, and we have tested the predictions of two competing models for C-H activation in the context of alcohol dehydrogenase. The kinetic isotope effects (KIEs) in this enzyme have previously suggested a model of quantum mechanical tunneling and coupled motion of primary (1°) and secondary (2°) hydrogens. Here we measure the 2° H/T KIEs with both H and D at the 1° position and find that the 2° KIE is significantly deflated with D-transfer, consistent with the predictions of recent Marcus-like models of H-transfer. The results suggest that the fast dynamics of H-tunneling result in a 1° isotope effect on the structure of the tunneling ready state: the trajectory of D-transfer goes through a shorter donor-acceptor distance than that of H-transfer.
authors.affiliation: Department of Chemistry, University of Iowa , Iowa City, Iowa 52242, United States.
authors.forename: Daniel
authors.initials: D
authors.lastname: Roston
authors.forename: Amnon
authors.initials: A
authors.lastname: Kohen
mesh_terms: D000426:Alcohol Dehydrogenase / Q000737:chemistry* / Q000378:metabolism; D019905:Benzyl Alcohol / Q000737:chemistry*; D008958:Models, Molecular; D010084:Oxidation-Reduction
chemical_list: D000426:Alcohol Dehydrogenase; D019905:Benzyl Alcohol
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