科研之友
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摘要
The physical mechanism of C-H bond activation by enzymes is the subject of intense study, and we have tested the predictions of two competing models for C-H activation in the context of alcohol dehydrogenase. The kinetic isotope effects (KIEs) in this enzyme have previously suggested a model of quantum mechanical tunneling and coupled motion of primary (1 degrees) and secondary (2 degrees) hydrogens. Here we measure the 2 degrees H/T KIEs with both H and D at the 1 degrees position and find that the 2 degrees KIE is significantly deflated with D-transfer, consistent with the predictions of recent Marcus-like models of H-transfer. The results suggest that the fast dynamics of H-tunneling result in a 1 degrees isotope effect on the structure of the tunneling ready state: the trajectory of D-transfer goes through a shorter donor acceptor distance than that of H-transfer.
- 出版日期2013-9-18
