The use of intramolecular isotope effects to distinguish between deprotonation and hydrogen atom abstraction mechanisms in cytochrome P-450- and peroxidase-catalyzed N-demethylation reactions.
The use of intramolecular isotope effects to distinguish between deprotonation and hydrogen atom abstraction mechanisms in cytochrome P-450- and peroxidase-catalyzed N-demethylation reactions.
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DOI：
10.1016/s0021-9258(17)43882-8
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发表时间：
1983-12
期刊：
影响因子：
--
通讯作者：
G. Miwa;J. Walsh;G. L. Kedderis;P. Hollenberg
中科院分区：
文献类型：
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作者：
G. Miwa;J. Walsh;G. L. Kedderis;P. Hollenberg
研究了细胞色素P-450同工酶和几种过氧化物酶催化n -甲基- n -三氘甲基苯胺n -去甲基化的分子内同位素效应，以区分去质子化和氢原子提取步骤。乳酸过氧化物酶、血红蛋白、肌红蛋白和辣根过氧化物酶的两种同工酶催化氢过氧化物依赖的n-去甲基化，初始速率从20到1700分钟不等。这些血红蛋白表现出较大的分子内同位素效应（kH/kD = 8.6 ~ 10.1）。相比之下，在相同条件下，细胞色素P-450同工酶和氯过氧化物酶（v = 1.5 ~ 1700 min-1）的同位素效应较低（kH/kD = 1.7 ~ 3.1）。过氧化氢酶表现出中间的分子内同位素效应（kH/kD = 5.4）。这些结果表明，所研究的大多数血红蛋白通过α -碳氢原子提取催化n -去甲基化反应，而细胞色素P-450和氯过氧化物酶催化的反应则通过α -碳去质子化进行。
Intramolecular isotope effects were determined for the N-demethylation of N-methyl-N-trideuteriomethylaniline catalyzed by two isozymes of cytochrome P-450 and several peroxidases in order to differentiate between deprotonation and hydrogen atom abstraction steps. Lactoperoxidase, hemoglobin, myoglobin, and two isozymes of horseradish peroxidase catalyzed the hydroperoxide-dependent N-demethylation at initial rates ranging from 20 to 1700 min-1. These hemeproteins exhibited large and comparable intramolecular isotope effects (kH/kD = 8.6 to 10.1). In contrast, two isozymes of cytochrome P-450 as well as chloroperoxidase (v = 1.5 to 1700 min-1) gave low isotope effects (kH/kD = 1.7 to 3.1) under identical conditions. Catalase exhibited an intermediate intramolecular isotope effect (kH/kD = 5.4). These results have been interpreted to indicate that most of the hemeproteins investigated catalyze N-demethylation reactions via alpha-carbon hydrogen atom abstraction, while the reactions catalyzed by cytochrome P-450 and chloroperoxidase proceed via alpha-carbon deprotonation.