Cleland W W
Institute for Enzyme Research, University of Wisconsin, Madison 53705.
Biochemistry. 1990 Apr 3;29(13):3194-7. doi: 10.1021/bi00465a006.
A number of enzymatic reactions involve intermediates that are not normally released during the reaction. Whether such an intermediate when added to the enzyme reacts as fast or faster than the normal substrates, and thus is "kinetically competent", depends on the degree to which the equilibrium constant for forming the intermediate from the substrates is different on the enzyme surface and in solution, as well as on the relative affinities of the enzyme for substrate and intermediate. Similar values for these equilibrium constants require that the intermediate react slowly, while a far more favorable value for intermediate formation on the enzyme allows the intermediate to react at up to the diffusion-limiting rate. When one intermediate is formed from two substrates, it may react much more rapidly than when two intermediates are formed from two substrates, or one from one. Comparison of the kinetics of the putative intermediate(s) and the substrate(s) can reveal a great deal about the mechanism of the catalytic reaction and the kinetic barrier that normally keeps the intermediate(s) on the enzyme.
许多酶促反应涉及在反应过程中通常不会释放的中间体。当将这样的中间体添加到酶中时，它是否能像正常底物一样快速或更快地反应，从而具有“动力学活性”，取决于从底物形成中间体的平衡常数在酶表面和溶液中的差异程度，以及酶对底物和中间体的相对亲和力。这些平衡常数的相似值要求中间体反应缓慢，而在酶上形成中间体的更有利值则允许中间体以高达扩散限制速率的速度反应。当由两种底物形成一种中间体时，它可能比由两种底物形成两种中间体或一种底物形成一种中间体时反应快得多。对假定中间体和底物的动力学进行比较，可以揭示出许多关于催化反应机制以及通常使中间体保留在酶上的动力学障碍的信息。
