High-affinity nitrosamine dealkylase system in rat liver microsomes and its induction by fasting.
High-affinity nitrosamine dealkylase system in rat liver microsomes and its induction by fasting.
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发表时间：
1983-02
期刊：
影响因子：
11.2
通讯作者：
Y. Y. Tu-Y.;Chung S. Yang
中科院分区：
文献类型：
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作者：
Y. Y. Tu-Y.;Chung S. Yang
为阐明亚硝胺代谢的酶学基础，本文研究了大鼠肝微粒体对亚硝胺的体外代谢及禁食对微粒体酶的影响。禁食1至3天导致烟酰胺腺嘌呤二核苷酸磷酸依赖性亚硝基二甲胺脱甲基酶（NDMAD）活性降低2至3倍。然而，细胞色素P-450含量和还原型烟酰胺腺嘌呤二核苷酸磷酸-细胞色素P-450还原酶和苄非他明脱甲基酶的活性仅略有增加。凝胶电泳分析揭示了禁食期间50，000-道尔顿蛋白质条带的诱导。该蛋白条带的诱导以及NDMAD活性的增强被CoCl 2和蛋白质和RNA生物合成的抑制剂抑制。微粒体还原型烟酰胺腺嘌呤二核苷酸磷酸-细胞色素P-450还原酶是脱甲基酶活性所必需的，这一事实支持细胞色素P-450参与NDMAD。动力学分析表明，低Km形式的NDMAD（表观Km，0.07 mM）是显着诱导禁食。与对照大鼠的微粒体，有至少三个表观Km值（0.07，0.38和38.6 mM）NDMAD，但与禁食大鼠的微粒体，低Km（0.07 mM）的形式是占主导地位的。这些结果表明，大鼠肝微粒体中含有一种对亚硝基二甲胺具有高亲和力的细胞色素P-450同工酶，且该同工酶受禁食诱导。除了亚硝基二甲胺，N-亚硝基-N-甲基乙胺、N-亚硝基-N-甲基丁胺、N-亚硝基-N-甲基苯胺和N-亚硝基-N-甲基苄胺的氧化脱甲基作用也会因禁食而增强。然而，这些反应的增强和底物依赖性的程度不同于NDMAD。
In order to elucidate the enzymic basis of nitrosamine metabolism, the in vitro metabolism of nitrosamines by rat liver microsomes and the effects of fasting on the microsomal enzymes have been studied. Fasting for 1 to 3 days causes a 2- to 3-fold enhancement of the reduced nicotinamide adenine dinucleotide phosphate-dependent nitrosodimethylamine demethylase (NDMAD) activity. The cytochrome P-450 content and the activities of reduced nicotinamide adenine dinucleotide phosphate-cytochrome P-450 reductase and benzphetamine demethylase, however, are only modestly increased. Gel electrophoretic analysis reveals the induction of a 50,000-dalton protein band during fasting. The induction of this protein band as well as the enhancement of NDMAD activity are inhibited by CoCl2 and inhibitors of protein and RNA biosynthesis. The involvement of cytochrome P-450 in the NDMAD is supported by the fact that microsomal reduced nicotinamide adenine dinucleotide phosphate-cytochrome P-450 reductase is required for the demethylase activity. Kinetic analysis indicates that a low-Km form of NDMAD (apparent Km, 0.07 mM) is markedly induced by fasting. With microsomes of control rats, there are at least three apparent Km values (0.07, 0.38, and 38.6 mM) for NDMAD; but with microsomes of fasting rats, the low-Km (0.07 mM) form is predominant. These results suggest that rat liver microsomes contain a cytochrome P-450 isozyme which has high affinity for nitrosodimethylamine, and this isozyme is induced by fasting. In addition to nitrosodimethylamine, the oxidative demethylation of N-nitroso-N-methylethylamine, N-nitroso-N-methylbutylamine, N-nitroso-N-methylaniline, and N-nitroso-N-methylbenzylamine is also enhanced by fasting. The extent of enhancement and substrate dependency of these reactions, however, is different from that of NDMAD.