Beckmann J D, Frerman F E
Biochemistry. 1985 Jul 16;24(15):3913-21. doi: 10.1021/bi00336a016.
Electron-transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO) was purified to homogeneity from pig liver submitochondrial particles. It is comparable in molecular weight and general properties to ETF-QO from beef heart [Ruzicka, F. J., & Beinert, H. (1977) J. Biol. Chem. 252, 8440-8445], and the electron spin resonance signals of the reduced iron-sulfur cluster are essentially identical. ETF-QO catalyzes the transfer of electrons from electron-transfer flavoprotein (ETF) to nitro blue tetrazolium, with a sluggish reaction turnover number of about 10-30 min-1. In contrast, the enzyme rapidly disproportionates ETF semiquinone, with a turnover number of 200 s-1. The reverse reaction, comproportionation of oxidized and hydroquinone ETF, provides an enzymatic assay for ETF-QO with picomolar sensitivity. Equilibrium spectrophotometric titrations show that ETF-QO accepts a maximum of two electrons from ETF and accepts three electron equivalents from dithionite or by photochemical reduction. All electrons from the enzymatically or chemically reduced protein can be transferred to 2,3-dimethoxy-5-methyl-6-pentyl-1,4-benzoquinone (PB), and this reaction is readily reversible. Reduction of ETF-QO by 2,3-dimethoxy-5-methyl-6-pentyl-1,4-benzohydroquinone is pH dependent and indicates the enzyme to have a redox potential that decreases by 47 mV per pH unit. Therefore, ETF-QO binds one to two protons upon reduction. The EO' at pH 7.3 is 38 mV. The ability of ETF-QO to catalyze the equilibration of ETF redox states has been used to evaluate the equilibrium 2ETFsq + nH+ in equilibrium ETFox + ETFhq.(ABSTRACT TRUNCATED AT 250 WORDS)
电子传递黄素蛋白 - 泛醌氧化还原酶（ETF - QO）从猪肝亚线粒体颗粒中纯化至同质。其分子量和一般性质与牛心的ETF - QO相当[鲁齐卡，F. J.，& 贝纳特，H.（1977年）《生物化学杂志》252，8440 - 8445]，还原态铁硫簇的电子自旋共振信号基本相同。ETF - QO催化电子从电子传递黄素蛋白（ETF）转移至硝基蓝四唑，反应周转数约为10 - 30分钟⁻¹，反应缓慢。相比之下，该酶能快速使ETF半醌发生歧化反应，周转数为200秒⁻¹。氧化型和对苯二酚型ETF的逆反应——化学计量反应，为ETF - QO提供了具有皮摩尔灵敏度的酶促测定法。平衡分光光度滴定表明，ETF - QO最多从ETF接受两个电子，并从连二亚硫酸盐或通过光化学还原接受三个电子当量。酶促或化学还原蛋白中的所有电子均可转移至2,3 - 二甲氧基 - 5 - 甲基 - 6 - 戊基 - 1,4 - 苯醌（PB），且该反应易于逆转。2,3 - 二甲氧基 - 5 - 甲基 - 6 - 戊基 - 1,4 - 苯二酚对ETF - QO的还原作用依赖于pH值，表明该酶具有每pH单位降低47 mV的氧化还原电位。因此，ETF - QO在还原时结合一到两个质子。pH 7.3时的标准氧化还原电位为38 mV。ETF - QO催化ETF氧化还原态平衡的能力已被用于评估平衡式2ETFsq + nH⁺ ⇌ ETFox + ETFhq。（摘要截于250字）
