DETERMINATION OF THE REDOX PROPERTIES OF THE RIESKE [2FE-2S] CLUSTER OF BOVINE HEART BC1 COMPLEX BY DIRECT ELECTROCHEMISTRY OF A WATER-SOLUBLE FRAGMENT
DETERMINATION OF THE REDOX PROPERTIES OF THE RIESKE [2FE-2S] CLUSTER OF BOVINE HEART BC1 COMPLEX BY DIRECT ELECTROCHEMISTRY OF A WATER-SOLUBLE FRAGMENT
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DOI：
10.1111/j.1432-1033.1992.tb17235.x
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发表时间：
1992-09-15
期刊：
影响因子：
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通讯作者：
VONJAGOW, G
中科院分区：
文献类型：
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作者：
LINK, TA;HAGEN, WR;VONJAGOW, G
用循环伏安法测定了牛心线粒体bc 1复合物的Rieske [2Fe-2S]簇的氧化还原电位。在硝酸处理过的裸玻碳电极上，该片段产生了立即而稳定的准可逆响应。在pH 7.2、25 ℃和I为0.01 M时的中点电位为E（m）= +312 +/- 3 mV。该值在20 mV内对应于EPR监测的染料介导的氧化还原滴定的结果。随着离子强度的增加，中点电位随I的平方根线性下降，直到I = 2.5 M。根据阴极-阳极峰分离，计算出低离子强度下的非均相速率常数k度约为2 x 10（-3）cm/s;速率常数随离子强度的增加而增加。从中点电位的温度依赖性，标准反应熵计算为Δ S-degree = -155J。K-1在pH5.5 ~ 10范围内，中点电位随pH的变化规律为：pH = 1.5 ~ 1.0时，中点电位随pH的变化规律为：pH = 5.5 ~ 1.0时，中点电位随pH的变化规律为：pH = 1.5 ~ 1.0时。高于pH 7时，观察到氧化还原状态依赖的pK变化。曲线的斜率为- 120 mV/pH，高于pH 9，表明氧化蛋白质发生了两次去质子化。通过曲线拟合获得的氧化蛋白的pK（a）值分别为7.6和9.2。在氧化蛋白的光谱中也可以观察到pK（a，ox）约为7.5的基团。氧化还原依赖的铁/硫蛋白的pK值被认为是必不可少的半醌氧化在Q（O）中心的bc 1复合物。
The redox potential of the Rieske [2Fe-2S] cluster of the bc1 complex from bovine heart mitochondria was determined by cyclic voltammetry of a water-soluble fragment of the iron/sulfur protein. At the nitric-acid-treated bare glassy-carbon electrode, the fragment gave an immediate and stable quasi-reversible response. The midpoint potential at pH 7.2, 25-degrees-C and I of 0.01 M was E(m) = +312 +/- 3 mV. This value corresponds within 20 mV to results of an EPR-monitored dye-mediated redox titration. With increasing ionic strength, the midpoint potential decreased linearly with square-root I up to I = 2.5 M. From the cathodic-to-anodic peak separation, the heterogeneous rate constant, k-degrees, was calculated to be approximately 2 x 10(-3) cm/s at low ionic strength; the rate constant increased with increasing ionic strength. From the temperature dependence of the midpoint potential, the standard reaction entropy was calculated as DELTAS-degrees = -155J . K-1 . mol-1.The pH dependence of the midpoint potential was followed over pH 5.5 - 10. Above pH 7, redox-state-dependent pK changes were observed. The slope of the curve, - 120 mV/pH above pH 9, indicated two deprotonations of the oxidized protein. The pK(a) values of the oxidized protein, obtained by curve fitting, were 7.6 and 9.2, respectively. A group with a pK(a,ox) of approximately 7.5 could also be observed in the optical spectrum of the oxidized protein. Redox-dependent pK values of the iron/sulfur protein are considered to be essential for semiquinone oxidation at the Q(o) center of the bc1 complex.