Oxygen isotope effects on electron transfer to O2 probed using chemically modified flavins bound to glucose oxidase.
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.
Roth
Justine P
JP
Department of Chemistry, University of California, Berkeley, California 94720, USA. jproth@jhu.edu
Wincek
Roseanne
R
Nodet
Gabrielle
G
Edmondson
Dale E
DE
McIntire
William S
WS
Klinman
Judith P
JP
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
D005415:Flavins; D010103:Oxygen Isotopes; D005182:Flavin-Adenine Dinucleotide; D005949:Glucose Oxidase; D010100:Oxygen