Oxygen Isotope Effects on Electron Transfer to O2 Probed Using Chemically Modified Flavins Bound to Glucose Oxidase
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- 作者：Justine P. Roth ; Roseanne Wincek ; Gabrielle Nodet ; Dale E. Edmondson ; William S. McIntire ; and Judith P. Klinman
- 刊名：Journal of the American Chemical Society
- 出版年：2004
- 出版时间：November 24, 2004
- 年：2004
- 卷：126
- 期：46
- 页码：15120 - 15131
- 全文大小：169K
- 年卷期：v.126,no.46(November 24, 2004)
- ISSN：1520-5126
文摘
Apo-glucose oxidase has been reconstituted with flavins modified in the 7 and 8 positions andcharacterized with regard to the catalytic rate of O2 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 O2 of
= 28 kcal mol-1 at optimal pH, which is similar to the value obtained earlier from temperature dependenciesof 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) to1.0279(6), apparently because of the dominant contribution of outer-sphere reorganization to the activationbarrier; within the context of semiclassical and quantum mechanical electron transfer theories, the magnitudeof the isotope effects reveals the importance of nuclear tunneling.
= 28 kcal mol-1 at optimal pH, which is similar to the value obtained earlier from temperature dependenciesof 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) to1.0279(6), apparently because of the dominant contribution of outer-sphere reorganization to the activationbarrier; within the context of semiclassical and quantum mechanical electron transfer theories, the magnitudeof the isotope effects reveals the importance of nuclear tunneling.