title: Oxygen isotope effects on electron transfer to O2 probed using chemically modified flavins bound to glucose oxidase.
abstract: Apo-glucose oxidase has been reconstituted with flavins modified in the 7 and 8 positions and characterized with regard to the catalytic rate of O(2) reduction and oxygen-18 isotope effects on this process. Kinetic studies as a function of driving force indicate a reorganization energy for electron transfer to O(2) of lambda = 28 kcal mol(-)(1) at optimal pH, which is similar to the value obtained earlier from temperature dependencies of rates (Roth, J. P.; Klinman, J. P. Proc. Natl. Acad. Sci. U.S.A. 2003, 100, 62-67). For the various enzyme-bound flavins, competitive oxygen-18 kinetic isotope effects fall within the narrow range of 1.0266(5) to 1.0279(6), apparently because of the dominant contribution of outer-sphere reorganization to the activation barrier; within the context of semiclassical and quantum mechanical electron transfer theories, the magnitude of the isotope effects reveals the importance of nuclear tunneling.
authors.affiliation: Department of Chemistry, University of California, Berkeley, California 94720, USA. jproth@jhu.edu
authors.forename: Justine P
authors.initials: JP
authors.lastname: Roth
authors.forename: Roseanne
authors.initials: R
authors.lastname: Wincek
authors.forename: Gabrielle
authors.initials: G
authors.lastname: Nodet
authors.forename: Dale E
authors.initials: DE
authors.lastname: Edmondson
authors.forename: William S
authors.initials: WS
authors.lastname: McIntire
authors.forename: Judith P
authors.initials: JP
authors.lastname: Klinman
mesh_terms: D001234:Aspergillus niger / Q000201:enzymology; D005182:Flavin-Adenine Dinucleotide / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism; D005415:Flavins / Q000737:chemistry* / Q000378:metabolism; D005949:Glucose Oxidase / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry* / Q000378:metabolism; D010103:Oxygen Isotopes; D011789:Quantum Theory; D013816:Thermodynamics
chemical_list: D005415:Flavins; D010103:Oxygen Isotopes; D005182:Flavin-Adenine Dinucleotide; D005949:Glucose Oxidase; D010100:Oxygen