The electric field generated by photosynthetic reaction center induces rapid reversed electron transfer in the bc1 complex.
The electric field generated by photosynthetic reaction center induces rapid reversed electron transfer in the bc1 complex.
复制标题
光合反应中心产生的电场诱导bc1复合体中快速反向电子转移。
作者：
V. P. Shinkarev;A. Crofts;C. Wraight
细胞色素bc（1）复合物是呼吸和光合作用电子传递链的中心酶。它将醌醇氧化和细胞色素还原的氧化还原功耦合到ATP合成所需的质子梯度的产生。当醌处理Q（i）-和Q（o）-网站的复合物被抑制的抗霉素和myxothiazol，闪光诱导的动力学的b-血红素链，在这些网站之间转移电子，预计也将受到抑制。然而，我们已经在类球红细菌色素体中观察到，当一部分血红素B（H）被还原时，闪光激发诱导血红素B（H）的快速氧化（半衰期约为0.1 ms），即使在抗霉素和粘噻唑存在下也是如此。这种氧化对离子载体和解偶联剂的敏感性，以及在这种反应的开始中没有任何延迟，表明这是由于B（L）和B（H）血红素之间的电子转移的逆转，由光合反应中心产生的电场驱动。在存在抗霉素A但不存在粘噻唑的情况下，第二次和随后的闪光诱导第一次闪光中还原的约10%的细胞色素B（H）的类似（约0.1 ms）瞬时氧化。根据观察到的场诱导血红素B（H）氧化的幅度，我们估计在pH 7时，血红素B（L）和B（H）之间共享一个电子的平衡常数为10-15。这个平衡常数的小值改变了我们对Q循环热力学的理解，特别是在bc（1）复合物的二聚体结构的背景下。
The cytochrome bc(1) complex is the central enzyme of respiratory and photosynthetic electron-transfer chains. It couples the redox work of quinol oxidation and cytochrome reduction to the generation of a proton gradient needed for ATP synthesis. When the quinone processing Q(i)- and Q(o)-sites of the complex are inhibited by both antimycin and myxothiazol, the flash-induced kinetics of the b-heme chain, which transfers electrons between these sites, are also expected to be inhibited. However, we have observed in Rhodobacter sphaeroides chromatophores, that when a fraction of heme b(H) is reduced, flash excitation induces fast (half-time approximately 0.1 ms) oxidation of heme b(H), even in the presence of antimycin and myxothiazol. The sensitivity of this oxidation to ionophores and uncouplers, and the absence of any delay in the onset of this reaction, indicates that it is due to a reversal of electron transfer between b(L) and b(H) hemes, driven by the electrical field generated by the photosynthetic reaction center. In the presence of antimycin A, but absence of myxothiazol, the second and following flashes induce a similar ( approximately 0.1 ms) transient oxidation of approximately 10% of the cytochrome b(H) reduced on the first flash. From the observed amplitude of the field-induced oxidation of heme b(H), we estimate that the equilibrium constant for sharing one electron between hemes b(L) and b(H) is 10-15 at pH 7. The small value of this equilibrium constant modifies our understanding of the thermodynamics of the Q-cycle, especially in the context of a dimeric structure of bc(1) complex.