Evidence To Support the Hypothesis That Promoting Vibrations Enhance the Rate of an Enzyme Catalyzed H-Tunneling Reaction

详细信息    查看全文

• 作者：Christopher R Pudney ; Sam Hay ; Colin Levy ; Jiayun Pang ; Michael J Sutcliffe ; David Leys ; Nigel S. Scrutton
• 刊名：Journal of the American Chemical Society
• 出版年：2009
• 出版时间：December 2, 2009
• 年：2009
• 卷：131
• 期：47
• 页码：17072-17073
• 全文大小：132K
• 年卷期：v.131,no.47(December 2, 2009)
• ISSN：1520-5126

文摘

In recent years there has been a shift away from transition state theory models for H-transfer reactions. Models that incorporate tunneling as the mechanism of H-transfer are now recognized as a better description of such reactions. Central to many models of H-tunneling is the notion that specific vibrational modes of the protein and/or substrate can increase the probability of a H-tunneling reaction, modes that are termed promoting vibrations. Thus far there has been limited evidence that promoting vibrations can increase the rate of H-transfer. In the present communication we examine the single hydride transfer from both NADPH and NADH to FMN in the reductive half-reaction of pentaerythritol tetranitrate reductase (PETNR). We find that there is a significant promoting vibration with NADPH but not with NADH and that the observed rate of hydride transfer is significantly (15×) faster with NADPH. We rule out differences in rate due to variation in driving force and the donor−acceptor distance, suggesting it is the promoting vibration with NADPH that is the origin of the increased observed rate. This study therefore provides direct evidence that promoting vibrations can lead to an increase in rate.