Chen G P, Ziegler D M
Department of Chemistry and Biochemistry, University of Texas at Austin 78712.
Arch Biochem Biophys. 1994 Aug 1;312(2):566-72. doi: 10.1006/abbi.1994.1346.
Eight commercially available selenides, a selenol, and selenourea were examined for substrate activity with purified pig liver flavin-containing monooxygenase (FMO). While none of the aromatic heterocyclic selenides tested showed detectable activity, all dialkyl- and alkylaryl-selenides free from ionic groups stimulated NADPH- and FMO-dependent oxygen uptake. With limiting substrate the molar ratio of oxygen reduced to selenide added was 1:1. Analysis of products from N-[2-(methylseleno)ethyl]benzamide demonstrated that the selenide was quantitatively oxidized to selenoxide. Further oxidation of either the FMO-generated or synthetic selenoxides was not detected. The dialkyl- and alkylaryl-selenoxides are potent thiol oxidants and reaction rates for the oxidation of thiols by methylphenylselenoxide and N-[2-(methylseleninyl)ethyl]benzamide followed second order kinetics with rate constants from 3-4 x 10(3) M-1 s-1 at pH 7.4, 37 degrees C. The rapid oxidation of thiols by these selenoxides demonstrates that the oxidation of selenides to selenoxides catalyzed by crude tissue preparations can be measured by following selenide-dependent oxidation of thiocholine by the procedure described earlier for the oxidation of thiourea (WXA Guo and D. M. Ziegler, 1991, Anal. Biochem. 198, 143-148). Activity measurements by this procedure indicated that the oxidation of dialkyl selenides by rat, guinea pig, or pig liver microsomes was catalyzed primarily by a monooxygenase with the properties of FMO. However, from 20 to 40% of the microsome-catalyzed oxidation of selenides bearing aryl substituents was sensitive to N-benzylimidazole, suggesting that P450-dependent monooxygenases also contribute, at least in part, to the oxidation of these xenobiotics.
研究了八种市售硒化物、一种硒醇和硒脲对纯化的猪肝含黄素单加氧酶（FMO）的底物活性。虽然所测试的芳香族杂环硒化物均未显示出可检测到的活性，但所有不含离子基团的二烷基和烷基芳基硒化物均能刺激NADPH和FMO依赖的氧摄取。在底物有限的情况下，消耗的氧与添加的硒化物的摩尔比为1:1。对N-[2-(甲基硒基)乙基]苯甲酰胺的产物分析表明，硒化物被定量氧化为硒氧化物。未检测到FMO生成的或合成的硒氧化物的进一步氧化。二烷基和烷基芳基硒氧化物是有效的硫醇氧化剂，在pH 7.4、37℃下，甲基苯硒氧化物和N-[2-(甲基亚硒酰基)乙基]苯甲酰胺氧化硫醇的反应速率遵循二级动力学，速率常数为3 - 4×10³ M⁻¹ s⁻¹。这些硒氧化物对硫醇的快速氧化表明，粗制组织制剂催化的硒化物氧化为硒氧化物的过程可以通过按照先前描述的硫脲氧化方法（WXA Guo和D.M. Ziegler，1991，《分析生物化学》198，143 - 148）跟踪硫代胆碱的硒化物依赖性氧化来测定。通过该方法进行的活性测量表明，大鼠、豚鼠或猪肝微粒体对二烷基硒化物的氧化主要由具有FMO性质的单加氧酶催化。然而，带有芳基取代基的硒化物的微粒体催化氧化中，有20%至40%对N-苄基咪唑敏感，这表明P450依赖的单加氧酶也至少部分地参与了这些外源化合物的氧化。
