Ugulava N B, Crofts A R
Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana 61801, USA.
FEBS Lett. 1998 Dec 4;440(3):409-13. doi: 10.1016/s0014-5793(98)01493-8.
The redox potential of the Rieske Fe-S protein has been investigated using circular dichroism (CD)-spectroscopy. The CD features characteristic of the purified bc1 complex and membranes of Rhodobacter sphaeroides were found in the region between 450 and 550 nm. The difference between reduced and oxidized CD-spectra shows a negative band at about 500 nm with a half of width 30 nm that corresponds to the specific dichroic absorption of the reduced Rieske protein (Fee, J.A. et al. (1984) J. Biol. Chem. 259, 124-133; Degli Esposti, M. et al. (1987) Biochem. J. 241, 285-290; Rich, P.R. and Wiggins, T.E. (1992) Biochem. Soc. Trans. 20, 241S). It was found that the redox potential at pH 7.0 for the Rieske center in the isolated bc1 complex and in chromatophore membranes from the R-26 strain of Rh. sphaeroides is 300 +/- 5 mV. In chromatophores from the BC17C strain of Rh. sphaeroides, the Em value measured for the Rieske iron-sulfur protein (ISP) was higher (315 +/- 5 mV), but the presence of carotenoids made measurement less accurate. The Em varied with pH in the range above pH 7, and the pH dependence was well fit either by one pK at approximately 7.5 in the range of titration, or by two pK values, pK1 = 7.6 and pK2 = 9.8. Similar titrations and pK values were found for the Rieske Fe-S protein in the isolated bc1 complex and membranes from the R-26 strain of Rb. sphaeroides. The results are discussed in the context of the mechanism of quinol oxidation by the bc1 complex, and the role of the iron sulfur protein in formation of a reaction complex at the Qo-site.
已使用圆二色性（CD）光谱法研究了 Rieske 铁硫蛋白的氧化还原电位。在 450 至 550 nm 区域发现了纯化的 bc1 复合物和球形红杆菌膜所特有的 CD 特征。还原态和氧化态 CD 光谱之间的差异在约 500 nm 处显示出一个负带，半高宽为 30 nm，这对应于还原态 Rieske 蛋白的特定二色性吸收（Fee, J.A. 等人（1984 年）《生物化学杂志》259, 124 - 133；Degli Esposti, M. 等人（1987 年）《生物化学杂志》241, 285 - 290；Rich, P.R. 和 Wiggins, T.E.（1992 年）《生物化学学会会报》20, 241S）。结果发现，在 pH 7.0 时，来自球形红杆菌 R - 26 菌株的分离 bc1 复合物和载色体膜中 Rieske 中心的氧化还原电位为 300 ± 5 mV。在球形红杆菌 BC17C 菌株的载色体中，测得的 Rieske 铁硫蛋白（ISP）的 Em 值较高（315 ± 5 mV），但类胡萝卜素的存在使测量不太准确。在 pH 高于 7 的范围内，Em 随 pH 变化，在滴定范围内，pH 依赖性可以用大约 7.5 处的一个 pK 很好地拟合，或者用两个 pK 值，pK1 = 7.6 和 pK2 = 9.8 拟合。在来自球形红杆菌 Rb. sphaeroides R - 26 菌株的分离 bc1 复合物和膜中，Rieske 铁硫蛋白也发现了类似的滴定和 pK 值。将结合 bc1 复合物氧化喹啉的机制以及铁硫蛋白在 Qo 位点反应复合物形成中的作用来讨论这些结果。
