While the underlying chemistry of enzyme-catalyzed reactions may be almost identical, the actual turnover rates of different substrates can vary significantly. This is seen in the turnover rates for the catalyzed hydrolysis of organophosphates by the bacterial phosphotriesterase OpdA. We investigate the variation in turnover rates by examining the hydrolysis of three classes of substrates: phosphotriesters, phosphothionates, and phosphorothiolates. Theoretical calculations were used to analyze the reactivity of these substrates and the energy barriers to their hydrolysis. This information was then compared to information derived from enzyme kinetics and crystallographic studies, providing new insights into the mechanism of this enzyme. We demonstrate that the enzyme catalyzes the hydrolysis of organophosphates through steric constraint of the reactants, and that the equilibrium between productively and unproductively bound substrates makes a significant contribution to the turnover rate of highly reactive substrates. These results highlight the importance of correct orientation of reactants within the active sites of enzymes to enable efficient catalysis.
尽管酶催化反应的
化学本质可能几乎相同,但不同底物的实际转换速率可能会有显著差异。这一点在细菌
磷酸三
酯酶OpdA催化有机
磷酸酯的
水解反应的转换速率中得到了体现。我们通过研究三类底物(
磷酸三酯、
磷硫酸酯和
磷硫酸酯)的
水解反应,来探讨转换速率的差异。我们利用理论计算来分析这些底物的反应活性及其
水解的能垒。然后将这些信息与从酶动力学和结晶学研究中得出的信息进行比较,从而对该酶的机制提供了新的见解。我们证明了该酶通过反应物的空间限制催化有机
磷酸酯的
水解,且有效结合和无效结合底物之间的平衡对高反应性底物的转换速率有显著贡献。这些结果强调了反应物在酶活性位点内正确取向的重要性,以实现高效的催化作用。