Job D, Dunford H B
Eur J Biochem. 1976 Jul 15;66(3):607-14. doi: 10.1111/j.1432-1033.1976.tb10588.x.
A stopped-flow kinetic study shows that the reduction rate of horseradish peroxidase compound I by phenols and aromatic amines is greatly dependent upon the substituent effect on the benzene ring. Morever it has been possible to relate the reduction rate constants of monosubstituted substrates by a linear free-energy relationship (Hammett equation). The correlation of log (rate constants) with sigma values (Hammett equation) and the absence of correlation with sigma+ values (Okamoto-Brown equation) can be explained by a mechanism of aromatic substrate oxidations, in which the substrate gives an electron to the enzyme compound I and simultaneously loses a proton. The analogy which has been made with oxidation potentials of phenols or anilines strengthens the view that the reaction is only dependent on the relative ease of oxidation of the substrate. The rate constant obtained for p-aminophenol indicates that a value of 2.3 X 10(8) M-1 S-1 probably approaches the diffusion-controlled limit for a bimolecular reaction involving compound I and an aromatic substrate.
一项停流动力学研究表明，酚类和芳香胺对辣根过氧化物酶化合物I的还原速率在很大程度上取决于苯环上的取代基效应。此外，通过线性自由能关系（哈米特方程）可以将单取代底物的还原速率常数联系起来。对数（速率常数）与σ值（哈米特方程）的相关性以及与σ+值（冈本-布朗方程）缺乏相关性，可以用芳香底物氧化的机制来解释，即底物向酶化合物I提供一个电子，同时失去一个质子。与酚类或苯胺的氧化电位所做的类比强化了这样一种观点，即该反应仅取决于底物氧化的相对难易程度。对氨基苯酚得到的速率常数表明，2.3×10⁸ M⁻¹ s⁻¹的值可能接近涉及化合物I和芳香底物的双分子反应的扩散控制极限。
