The iron-sulfur cluster of electron transfer flavoprotein-ubiquinone oxidoreductase is the electron acceptor for electron transfer flavoprotein.
The iron-sulfur cluster of electron transfer flavoprotein-ubiquinone oxidoreductase is the electron acceptor for electron transfer flavoprotein.
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DOI：
10.1021/bi800507p
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发表时间：
2008-08-26
期刊：
影响因子：
2.9
通讯作者：
Eaton SS
中科院分区：
文献类型：
--
作者：
Swanson MA;Usselman RJ;Frerman FE;Eaton GR;Eaton SS
电子转移黄素蛋白-泛醌氧化还原酶（ETF-QO）接受电子转移黄素蛋白（ETF）的电子并还原泛醌库中的泛醌。它含有一个[4Fe-4S]2+，1+和一个FAD，它们在分离的氧化酶中是抗磁性的，可以被酶供体或连二亚硫酸盐还原为顺磁性形式。在猪蛋白中，苏氨酸367与FAD的黄素环的N1和O2氢键合。类球红细菌ETF-QO中的类似位点是天冬酰胺338。将突变体N338 T和N338 A导入R.通过定点诱变对类球形菌蛋白进行修饰，以确定该位点处的氢键对氧化还原电位和活性的影响。这些突变并没有改变光谱、EPR g值、自旋-晶格弛豫速率或[4Fe-4S]2+，1+到FAD点-偶极间的自旋距离。突变对铁硫簇合物的还原电位没有影响，这是通过在15 K下[4Fe-4S]+的连续波EPR信号的变化来监测的。对于FAD半醌，通过在100或293 K下监测滴定得到显著不同的电位。基于293 K下的光谱，N338 T突变使FAD的第一和第二中点电位分别从野生型的+47 mV和−30 mV变为−11 mV和−19 mV。N338 A突变将电位降低至−37 mV和−49 mV。降低中点电位导致醌还原酶活性降低，对ETF-QO催化的ETF 1 e −的反硝化作用的影响可忽略不计。这些观察结果表明，FAD参与电子转移到泛醌，但不参与从ETF到ETF-QO的电子转移。因此，铁硫簇是ETF的直接受体。
Electron-transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO) accepts electrons from electron-transfer flavoprotein (ETF) and reduces ubiquinone from the ubiquinone-pool. It contains one [4Fe-4S]2+,1+ and one FAD, which are diamagnetic in the isolated oxidized enzyme and can be reduced to paramagnetic forms by enzymatic donors or dithionite. In the porcine protein, threonine 367 is hydrogen bonded to N1 and O2 of the flavin ring of the FAD. The analogous site in Rhodobacter sphaeroides ETF-QO is asparagine 338. Mutations N338T and N338A were introduced into the R. sphaeroides protein by site-directed mutagenesis to determine the impact of hydrogen bonding at this site on redox potentials and activity. The mutations did not alter the optical spectra, EPR g-values, spin-lattice relaxation rates, or the [4Fe-4S]2+,1+ to FAD point-dipole interspin distances. The mutations had no impact on the reduction potential for the iron-sulfur cluster, which was monitored by changes in the continuous wave EPR signals of the [4Fe-4S]+ at 15 K. For the FAD semiquinone, significantly different potentials were obtained by monitoring the titration at 100 or 293 K. Based on spectra at 293 K the N338T mutation shifted the first and second midpoint potentials for the FAD from +47 mV and −30 mV for wild type to −11 mV and −19 mV, respectively. The N338A mutation decreased the potentials to −37 mV and −49 mV. Lowering the midpoint potentials resulted in a decrease in the quinone reductase activity and negligible impact on disproportionation of ETF1e− catalyzed by ETF-QO. These observations indicate that the FAD is involved in electron transfer to ubiquinone, but not in electron transfer from ETF to ETF-QO. Therefore the iron-sulfur cluster is the immediate acceptor from ETF.
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影响因子：
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通讯作者：
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