Roth Justine P, Wincek Roseanne, Nodet Gabrielle, Edmondson Dale E, McIntire William S, Klinman Judith P
Department of Chemistry, University of California, Berkeley, California 94720, USA.
J Am Chem Soc. 2004 Nov 24;126(46):15120-31. doi: 10.1021/ja047050e.
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.
已用在7位和8位修饰的黄素对脱辅基葡萄糖氧化酶进行了重组，并对其O₂还原催化速率以及该过程中的氧-18同位素效应进行了表征。作为驱动力函数的动力学研究表明，在最佳pH值下，电子转移至O₂的重组能λ = 28 kcal mol⁻¹，这与之前从速率的温度依赖性获得的值相似（罗斯，J.P.；克林曼，J.P.《美国国家科学院院刊》美国2003年，100，62 - 67）。对于各种与酶结合的黄素，竞争性氧-18动力学同位素效应落在1.0266(5)至1.0279(6)的窄范围内，这显然是由于外层重组对活化能垒的主要贡献；在半经典和量子力学电子转移理论的背景下，同位素效应的大小揭示了核隧穿的重要性。
