title: Experimental evidence for hydrogen tunneling when the isotopic arrhenius prefactor (A(H)/A(D)) is unity.
abstract: The temperature dependence of the kinetic isotope effect (KIE) is one of the major tools used for the investigation of hydrogen tunneling in condensed phase. Hydrogen transfer reactions displaying isotopic Arrhenius prefactor ratios (A(H)/A(D)) of unity are generally ascribed to a semiclassical mechanism. Here, we have identified a double mutant of soybean lipoxygenase (SLO-1, an enzyme previously shown to follow quantum mechanical hydrogen tunneling), that displays an A(H)/A(D) of unity and highly elevated (nonclassical) KIEs. This observation highlights the shortcoming of assigning a hydrogen transfer reaction to a semiclassical model based solely on an Arrhenius prefactor ratio.
authors.affiliation: Department of Chemistry and Molecular and Cell Biology, University of California, Berkeley, California 94720-1460, USA.
authors.forename: Sudhir C
authors.initials: SC
authors.lastname: Sharma
authors.forename: Judith P
authors.initials: JP
authors.lastname: Klinman
mesh_terms: D003903:Deuterium / Q000737:chemistry / Q000378:metabolism; D006859:Hydrogen / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D008084:Lipoxygenase / Q000737:chemistry* / Q000378:metabolism; D013696:Temperature; D013816:Thermodynamics
chemical_list: D006859:Hydrogen; D003903:Deuterium; C101084:lipoxygenase L-1; D008084:Lipoxygenase