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首页> 外文期刊>Biochimica et biophysica acta: BBA: International journal of biochemistry, biophysics and molecular biololgy. Proteins and Proteomics >Differential substrate behaviour of phenol and aniline derivatives during oxidation by horseradish peroxidase: kinetic evidence for a two-step mechanism
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Differential substrate behaviour of phenol and aniline derivatives during oxidation by horseradish peroxidase: kinetic evidence for a two-step mechanism

机译：辣根过氧化物酶氧化过程中苯酚和苯胺衍生物的不同底物行为：两步机理的动力学证据

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摘要

The catalytic constant (k_(cat)) and the second-order association constant of compound II with reducing substrate (k_5) of horseradish peroxidase C (HRPC) acting on phenols and anilines have been determined from studies of the steady-state reaction velocities (V_0 vs. [S_0]). Since k_(cat)=k_2k_6/k_2+k_6, and k_2 (the first-order rate constant for heterolytic cleavage of the oxygen–oxygen bond of hydrogen peroxide during compound I formation) is known, it has been possible to calculate the first-order rate constant for the transformation of each phenol or aniline by HRPC compound II (k_6). The values of k6 are quantitatively correlated to the σ values (Hammett equation) and can be rationalized by an aromatic substrate oxidation mechanism in which the substrate donates an electron to the oxyferryl group in HRPC compound II, accompanied by two proton additions to the ferryl oxygen atom, one from the substrate and the other the protein or solvent. k_6 is also quantitatively correlated to the experimentally determined ~(13)C-NMR chemical shifts (δ_1) and the calculated ionization potentials, E (HOMO), of the substrates. Similar dependencies were observed for kcat and k5. From the kinetic analysis, the absolute values of the Michaelis constants for hydrogen peroxide and the reducing substrates (KMH_2O_2 and KMS), respectively, were obtained.
机译：从稳态反应速度的研究中已经确定了化合物II与辣根过氧化物酶C（HRPC）对酚和苯胺的还原底物（k_5）的催化常数（k_（cat））和​​二阶缔合常数（ V_0与[S_0]）。由于已知k_（cat）= k_2k_6 / k_2 + k_6和k_2（化合物I形成过程中过氧化氢的氧-氧键的杂合裂解的一级速率常数），因此可以计算出一级HRPC化合物II（k_6）转化每种苯酚或苯胺的反应速率常数。 k6的值与σ值（Hammett方程）在数量上相关，并且可以通过芳香族底物氧化机理进行合理化，其中底物向HRPC化合物II中的羟基羟基提供电子，并向二氧杂环己烷中添加两个质子原子，一种来自底物，另一种来自蛋白质或溶剂。 k_6还与实验确定的底物的〜（13）C-NMR化学位移（δ_1）和计算出的电离电势E（HOMO）定量相关。对于kcat和k5也观察到类似的依赖性。通过动力学分析，分别获得了过氧化氢和还原性底物（KMH_2O_2和KMS）的米氏常数的绝对值。

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