Meinhardt S W, Gennis R B, Ohnishi T
Department of Biochemistry and Biophysics, School of Medicine, University of Pennsylvania, Philadelphia 19104.
Biochim Biophys Acta. 1989 Jun 23;975(1):175-84. doi: 10.1016/s0005-2728(89)80216-6.
We have examined the thermodynamic and EPR properties of one of the ubiquinol oxidase systems (the cytochrome d complex) of Escherichia coli, and have assigned the EPR-detectable signals to the optically identified cytochromes. The axial high spin g = 6.0 signal has been assigned to cytochrome d based on the physicochemical properties of this signal and those of the optically defined cytochrome d. A rhombic low spin species at gx,y,z = 1.85, 2.3, 2.5 exhibited similar properties but was present at only one-fifth the concentration of the axial high spin species. Both species have an Em7 of 260 mV and follow a -60 mV/pH unit dependence from pH 6 to 10. The rhombic high spin signal with gy,z = 5.5 and 6.3 has been assigned to cytochrome b-595. This component has an Em7 of 136 mV and follows a -30 mV/pH unit dependence from pH 6 to 10. Lastly, the low spin gz = 3.3 signal which titrates with an Em7 of 195 mV and follows a -40 mV/pH unit dependence from pH 6 to 10 has been assigned to cytochrome b-558. Spin quantitation of the high-spin signals indicates that cytochrome d and b-595 are present in approximately equal amounts. These observations are discussed in terms of the stoichiometry of the prosthetic groups and its implications on the mechanism of electron transport.
我们研究了大肠杆菌泛醇氧化酶系统之一（细胞色素d复合物）的热力学和电子顺磁共振（EPR）特性，并将EPR可检测信号与光学鉴定的细胞色素进行了对应。基于该信号以及光学定义的细胞色素d的物理化学性质，轴向高自旋g = 6.0信号已被确定为细胞色素d。在gx,y,z = 1.85、2.3、2.5处的菱形低自旋物种表现出相似的性质，但其浓度仅为轴向高自旋物种的五分之一。这两种物种的Em7均为260 mV，在pH值从6到10的范围内，其电位随pH值变化的斜率为-60 mV/pH单位。具有gy,z = 5.5和6.3的菱形高自旋信号已被确定为细胞色素b-595。该组分的Em7为136 mV，在pH值从6到10的范围内，其电位随pH值变化的斜率为-30 mV/pH单位。最后，低自旋gz = 3.3信号的Em7为195 mV，在pH值从6到10的范围内，其电位随pH值变化的斜率为-40 mV/pH单位，该信号已被确定为细胞色素b-558。高自旋信号的自旋定量表明，细胞色素d和b-595的含量大致相等。本文根据辅基的化学计量及其对电子传递机制的影响对这些观察结果进行了讨论。
