Furnes Bjarte, Schlenk Daniel
Environmental Toxicology Program, University of California, Riverside, California 92521, USA.
Toxicol Sci. 2004 Apr;78(2):196-203. doi: 10.1093/toxsci/kfh079. Epub 2004 Feb 19.
The flavin-containing monooxygenase gene family (FMO1-6) in humans encodes five functional isoforms that catalyze the monooxygenation of numerous N-, P- and S-containing drugs and toxicants. A previous single nucleotide polymorphism (SNP) analysis of FMO1 in African-Americans identified seven novel SNPs. To determine the functional relevance of the coding FMO1 variants (H97Q, I303V, I303T, R502X), they were heterologously expressed using a baculovirus system. Catalytic efficiency and stereoselectivity of N- and S-oxygenation was determined in the FMO1 variants using several substrates. The I303V variant showed catalytic constants equal to wild-type FMO1 for methimazole and methyl p-tolyl sulfide. Catalytic efficiency (V(max)/K(m)) of methyl p-tolyl sulfide oxidation by R502X was unaltered. In contrast, methimazole oxidation by R502X was not detected. Both H97Q and I303T had elevated catalytic efficiency with regards to methyl p-tolyl sulfide (162% and 212%, respectively), but slightly reduced efficiency with regards to methimazole (81% and 78%). All the variants demonstrated the same stereoselectivity for methyl p-tolyl sulfide oxidation as wild-type FMO1. FMO1 also metabolized the commonly used insecticide fenthion to its (+)-sulfoxide, with relatively high catalytic efficiency. FMO3 metabolized fenthion to its sulfoxide at a lower catalytic efficiency than FMO1 (27%) and with less stereoselectivity (74% (+)-sulfoxide). Racemic fenthion sulfoxide was a weaker inhibitor of acetylcholinesterase than its parent compound (IC(50) 0.26 and 0.015 mM, respectively). The (+)- and (-)-sulfoxides were equally potent inhibitors of acetylcholinesterase. These data indicate that all the currently known FMO1 variants are catalytically active, but alterations in kinetic parameters were observed.
人类含黄素单加氧酶基因家族（FMO1 - 6）编码五种功能性同工型，可催化众多含氮、磷和硫的药物及毒物的单加氧反应。先前对非裔美国人FMO1的单核苷酸多态性（SNP）分析鉴定出七个新的SNP。为了确定编码FMO1变体（H97Q、I303V、I303T、R502X）的功能相关性，使用杆状病毒系统对它们进行了异源表达。使用几种底物在FMO1变体中测定了氮和硫氧化的催化效率及立体选择性。I303V变体对甲巯咪唑和对甲苯基甲基硫醚的催化常数与野生型FMO1相当。R502X对对甲苯基甲基硫醚氧化的催化效率（V(max)/K(m)）未改变。相比之下，未检测到R502X对甲巯咪唑的氧化作用。H97Q和I303T对对甲苯基甲基硫醚的催化效率均有所提高（分别为162%和212%），但对甲巯咪唑的效率略有降低（分别为81%和78%）。所有变体对对甲苯基甲基硫醚氧化的立体选择性与野生型FMO1相同。FMO1还以相对较高的催化效率将常用杀虫剂倍硫磷代谢为其(+)-亚砜。FMO3将倍硫磷代谢为亚砜的催化效率低于FMO1（27%），且立体选择性较低（74% (+)-亚砜）。外消旋倍硫磷亚砜作为乙酰胆碱酯酶抑制剂的活性比其母体化合物弱（IC(50)分别为0.26和0.015 mM）。(+)-和(-)-亚砜作为乙酰胆碱酯酶抑制剂的效力相当。这些数据表明，所有目前已知的FMO1变体均具有催化活性，但动力学参数存在改变。
