COOXIDATION OF XENOBIOTICS BY THE PROSTAGLANDIN SYNTHETASE

前列腺素合成酶对异种生物的共氧化

• 批准号: 3777565
• 负责人: T E ELING
• 金额: --
• 依托单位: NATIONAL INSTITUTE OF ENVIRONMENTAL HEALTH SCIENCES
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/3777565
• 关键词: acetylation; chemical carcinogen; chemical carcinogenesis; cytotoxicity; electron spin resonance spectroscopy; environmental toxicology; enzyme mechanism; enzyme substrate; free radicals; molecular biology; mutagen testing; oxidation; prostaglandin endoperoxide synthase; toxin metabolism

The long range goal of this project is to study the oxidation of chemicals to toxic or carcinogenic metabolites by prostaglandin H synthase (PHS) and to demonstrate the importance of this enzyme system in chemical- induced toxicity or carcinogenesis. We have shown that aromatic amine carcinogens, are metabolized to mutagens by PHS. PHS dependent oxidation occurred by a free radical mechanism. Amines are first acetylated to the acetylamine. PHS but not HRP then metabolizes the acetylamine to nitroacetylamine. The nitro metabolites are potent direct acting mutagens. This explains the role of bacterial acetylation and the difference between PHS and HRP. Our data suggest that PHS is a versatile enzyme system that can catalyze a variety of reactions which are important in the conversion of chemicals to carcinogenic metabolites in extra hepatic tissue. We have continued our studies on the formation of tyrosyl radicals during the oxygenation of arachidonic acid by prostaglandin H synthase. Two tyrosyl radicals were observed by ESR that were characterized as radicals with two different conformations. Data obtained from recent experiments further suggest that these radicals are not catalytic intermediates but are formed during the process of self-inactivation that occurs during enzyme catalysis. Studies also indicate that the tryosyl radicals formed by PHS have a different reactivity than the tyrosyl radicals formed by ribonucleotide reductase suggesting that the radicals have very different and unrelated roles in enzyme catalysis. We have also continued our studies on the mechanism by which aromatic amines are oxidized by PHS. We have obtained addition data that suggest that for some carcinogenic amines that are poor peroxidase substrates that direct oxygen transfer from the enzyme to the amine occurs with the purified enzyme. With crude microsomal preparations both direct transfer and peroxyl radical mediated oxygenation occurred. Further studies are in process. Future direction is to use molecular biology techniques to generate mutant forms of PHS.

这个项目的长期目标是研究化学品的氧化 前列腺素H合酶（PHS）的毒性或致癌代谢产物 并证明这种酶系统在化学中的重要性- 诱发毒性或致癌作用。 我们已经证明，芳香胺 致癌物，通过PHS代谢为诱变剂。 PHS依赖 氧化通过自由基机制发生。 胺首先 乙酰化为乙酰胺。 PHS而不是HRP然后代谢 乙酰胺到硝基乙酰胺。 硝基代谢物是有效的直接 致突变剂 这解释了细菌乙酰化的作用， PHS和HRP的区别 我们的数据表明，小灵通是一个 多功能酶系统，可以催化多种反应， 重要的化学品转化为致癌代谢物， 肝外组织 我们继续研究酪氨酰自由基的形成， 花生四烯酸被前列腺素H合酶氧化。 两 ESR检测到酪氨酰自由基，其特征为自由基 有两种不同的构象 从最近的实验中获得的数据 进一步表明，这些自由基不是催化中间体， 在酶的自我失活过程中形成 催化作用 研究还表明，由PHS形成的酪氨酸基 具有与酪氨酰基自由基不同的反应性， 核糖核苷酸还原酶，这表明自由基具有非常不同的 和不相关的酶催化作用。 我们还继续我们的 研究了PHS氧化芳香胺的反应机理。 我们已经获得了额外的数据表明，对于一些致癌物质， 胺是直接氧转移的不良过氧化物酶底物 从酶到胺的转化是在纯化的酶中进行的。 与 直接转移和过氧自由基的粗微粒体制备物 发生介导的氧合。 进一步的研究正在进行中。 未来 方向是利用分子生物学技术产生突变形式 的PHS。