Guallar Victor, Friesner Richard A
Department of Chemistry and Center for Biomolecular Simulations, Columbia University, New York, New York 10027, USA.
J Am Chem Soc. 2004 Jul 14;126(27):8501-8. doi: 10.1021/ja036123b.
The catalytic pathway of cytochrome P450cam is studied by means of a hybrid quantum mechanics/molecular mechanics method. Our results reveal an active role of the enzyme in the different catalytic steps. The protein initially controls the energy gap between the high- and low-spin states in the substrate binding process, allowing thermodynamic reduction by putidaredoxin reductase and molecular oxygen addition. A second electron reduction activates the delivery of protons to the active site through a selective interaction of Thr252 and the distal oxygen causing the O--O cleavage. Finally, the protein environment catalyzes the substrate hydrogen atom abstraction step with a remarkably low free energy barrier ( approximately 8 kcal/mol). Our results are consistent with the effect of mutations on the enzymatic efficacy and provide a satisfactory explanation for the experimental failure to trap the proposed catalytically competent species, a ferryl Fe(IV) heme.
通过一种量子力学/分子力学混合方法研究了细胞色素P450cam的催化途径。我们的结果揭示了该酶在不同催化步骤中的积极作用。在底物结合过程中，蛋白质最初控制高自旋态和低自旋态之间的能隙，从而允许通过恶臭假单胞菌铁氧还蛋白还原酶进行热力学还原并添加分子氧。第二次电子还原通过Thr252与远端氧的选择性相互作用激活质子向活性位点的传递，导致O-O键断裂。最后，蛋白质环境以极低的自由能垒（约8千卡/摩尔）催化底物氢原子提取步骤。我们的结果与突变对酶活性的影响一致，并为实验未能捕获所提出的催化活性物种——高铁血红素（Fe(IV)血红素）提供了令人满意的解释。
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