Rettie A E, Meier G P, Sadeque A J
Department of Medicinal Chemistry, University of Washington, Seattle 98195, USA.
Chem Biol Interact. 1995 Apr 28;96(1):3-15. doi: 10.1016/0009-2797(94)03579-w.
A homologous series of alkyl-substituted p-tolyl sulfides have been synthesized and evaluated as in vitro, isozyme-selective substrate probes for the microsomal flavin containing monooxygenases. Straight-chain and branched-chain alkyl homologs were metabolized to the corresponding (R)- and (S)-sulfoxides which were analyzed by chiral phase high-performance liquid chromatography. Initial studies demonstrated that the stereochemical composition of alkyl p-tolyl sulfoxides generated by FMO2, purified from rabbit lung, was a function of the degree of steric crowding about the prochiral center. In contrast, purified rabbit liver FMO1 formed the (R)-sulfoxide from the n-alkyl series of substrates in a highly stereoselective manner (> 90%). Similar results were obtained with these two rabbit cDNAs expressed in E. coli. In contrast to rabbit FMO1 and FMO2, a characteristic feature of catalysis by cDNA-expressed rabbit FMO3 was the lack of stereoselectivity observed for formation of methyl p-tolyl sulfoxide. Collectively, these data demonstrate that the stereochemical composition of sulfoxides generated from the n-alkyl series of sulfides is isozyme-dependent. Metabolism of methyl p-tolyl sulfide by detergent-solubilized hepatic microsomes from a wide variety of experimental animals yielded predominantly (R)- methyl p-tolyl sulfoxide, which, at least in rabbit liver, is indicative of catalysis dominated by FMO1. However, solubilized human and macaque liver preparations catalyzed this reaction in a relatively non-stereoselective manner. Macaque liver FMO was purified and the metabolite profile generated from the n-alkyl p-tolyl sulfides was found to be most similar to rabbit FMO3. Moreover, antibodies directed against macaque liver FMO selectively reacted with rabbit FMO3 and a microsomal protein expressed in adult human, but not fetal human liver, adult human kidney or adult human lung. Therefore, an FMO isoform expressed selectively in adult primate liver has catalytic and immunochemical properties consistent with its classification in the FMO3 family.
已合成了一系列烷基取代的对甲苯基硫醚，并将其作为微粒体含黄素单加氧酶的体外同工酶选择性底物探针进行了评估。直链和支链烷基同系物被代谢为相应的（R）-和（S）-亚砜，通过手性相高效液相色谱进行分析。初步研究表明，从兔肺中纯化的FMO2生成的烷基对甲苯基亚砜的立体化学组成是前手性中心周围空间拥挤程度的函数。相比之下，纯化的兔肝FMO1以高度立体选择性的方式（>90%）从正烷基系列底物中形成（R）-亚砜。在大肠杆菌中表达的这两种兔cDNA也得到了类似的结果。与兔FMO1和FMO2不同，cDNA表达的兔FMO3催化的一个特征是在形成甲基对甲苯基亚砜时缺乏立体选择性。总的来说，这些数据表明，正烷基系列硫化物生成的亚砜的立体化学组成是同工酶依赖性的。来自多种实验动物的去污剂增溶肝微粒体对甲基对甲苯基硫醚的代谢主要产生（R）-甲基对甲苯基亚砜，至少在兔肝中，这表明催化作用主要由FMO1主导。然而，增溶的人和猕猴肝制剂以相对非立体选择性的方式催化该反应。纯化了猕猴肝FMO，发现从正烷基对甲苯基硫醚产生的代谢物谱与兔FMO3最相似。此外，针对猕猴肝FMO的抗体与兔FMO3以及在成年人类而非胎儿人类肝脏、成年人类肾脏或成年人类肺中表达的一种微粒体蛋白发生选择性反应。因此，在成年灵长类肝脏中选择性表达的一种FMO同工酶具有与其在FMO3家族中的分类一致的催化和免疫化学特性。
