Anzenbacher P, Niwa T, Tolbert L M, Sirimanne S R, Guengerich F P
Department of Biochemistry, Vanderbilt University, Nashville, Tennessee 37232-0146, USA.
Biochemistry. 1996 Feb 27;35(8):2512-20. doi: 10.1021/bi952330f.
Variously substituted alkylanthracenes were studied as models for polycyclic hydrocarbon oxidations. 9-Methylanthracene was oxidized to 9-(hydroxymethyl)anthracene, 10-methyl-10-hydroxy-9-anthrone, and anthraquinone in several systems, including (i) NADPH- and O2-fortified rat liver microsomes, (ii) cytochrome P450 (P450) 2B1 Supported by either iodosylbenzene (PhIO) or a mixture of NADPH-P450 reductase, NADPH, and O2, (iii) horseradish peroxidase and either H2O2 or ethyl hydroperoxide, and (iv) a mixture of iron tetraphenylporphine (FeTPP) and PhIO (in anhydrous CH2Cl2/MeOH). The microsomal system also formed dihydrodiols from 9-methyl- and 9-ethylanthracenes. The formation of the three oxidized products by the P450/NADPH/O2 system was dependent upon O2 label from 18O2 was incorporated into the products, and no label from H2(18O) was incorporated. No label from 18O2 was incorporated into the three products in the FeTPP/PhIO system. In the horseradish peroxidase/H2O2 system, the formation of the three products was decreased when O2 was omitted, and label from both H2(18)O and 18O2 was incorporated into all three products. The results are interpreted in terms of three mechanisms. One is used by the FeTPP and P450 systems, with all oxygen transfers coming from an FeO entity. The other two pathways are utilized by horseradish peroxidase and begin with formation of a radical cation, which can undergo reactions either with H2O or with O2 to form the products detected here. The involvement of a 9-methylanthracene radical cation in the P450 and FeTPP pathways is a possibility, but rapid rearrangement and oxygen rebound must be invoked. Comparisons of products from various 9-alkylanthracenes do not provide evidence that one-electron oxidation is an integral part of the epoxidation process with these compounds. The significance of the lack of trapping of radical (by H2(18O) in the P450 reactions to DNA adduct formation is considered.
研究了各种取代的烷基蒽作为多环烃氧化的模型。在几个体系中，9-甲基蒽被氧化为9-(羟甲基)蒽、10-甲基-10-羟基-9-蒽酮和蒽醌，这些体系包括：(i) 用NADPH和O₂强化的大鼠肝微粒体；(ii) 由碘苯(PhIO)或NADPH-P450还原酶、NADPH和O₂的混合物支持的细胞色素P450 (P450) 2B1；(iii) 辣根过氧化物酶和H₂O₂或乙基过氧化氢；(iv) 四苯基卟啉铁(FeTPP)和PhIO的混合物(在无水二氯甲烷/甲醇中)。微粒体体系还从9-甲基蒽和9-乙基蒽形成二氢二醇。P450/NADPH/O₂体系形成的三种氧化产物取决于18O₂中的O₂标记被掺入产物中，而H₂(18O)中的标记未被掺入。在FeTPP/PhIO体系中，18O₂中的标记未被掺入这三种产物中。在辣根过氧化物酶/H₂O₂体系中，当省略O₂时，这三种产物的形成减少，并且H₂(18)O和18O₂中的标记都被掺入所有三种产物中。结果根据三种机制进行了解释。一种机制被FeTPP和P450体系使用，所有的氧转移都来自FeO实体。另外两种途径被辣根过氧化物酶利用，始于自由基阳离子的形成，该自由基阳离子可以与H₂O或O₂发生反应以形成此处检测到的产物。9-甲基蒽自由基阳离子可能参与P450和FeTPP途径，但必须调用快速重排和氧反弹。对各种9-烷基蒽产物的比较没有提供证据表明单电子氧化是这些化合物环氧化过程的一个组成部分。考虑了在P450反应中缺乏自由基捕获(通过H₂(18O))对DNA加合物形成的意义。
