Yu Chang-An, Cen Xiaowei, Ma He-Wen, Yin Ying, Yu Linda, Esser Lothar, Xia Di
Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, OK 74078, USA.
Biochim Biophys Acta. 2008 Jul-Aug;1777(7-8):1038-43. doi: 10.1016/j.bbabio.2008.03.033. Epub 2008 Apr 10.
Intensive biochemical, biophysical and structural studies of the cytochrome (cyt) bc(1) complex in the past have led to the formulation of the "protonmotive Q-cycle" mechanism for electron and proton transfer in this vitally important complex. The key step of this mechanism is the separation of electrons during the oxidation of a substrate quinol at the Q(P) site with both electrons transferred simultaneously to ISP and cyt b(L) when the extrinsic domain of ISP (ISP-ED) is located at the b-position. Pre-steady state fast kinetic analysis of bc(1) demonstrates that the reduced ISP-ED moves to the c(1)-position to reduce cyt c(1) only after the reduced cyt b(L) is oxidized by cyt b(H). However, the question of how the conformational switch of ISP-ED is initiated remains unanswered. The results obtained from analysis of inhibitory efficacy and binding affinity of two types of Q(P) site inhibitors, Pm and Pf, under various redox states of the bc(1) complex, suggest that the electron transfer from heme b(L) to b(H) is the driving force for the releasing of the reduced ISP-ED from the b-position to c(1)-position to reduce cyt c(1).
过去对细胞色素（cyt）bc(1)复合物进行的深入生化、生物物理和结构研究，促成了该极为重要的复合物中电子和质子转移的“质子动力Q循环”机制的形成。该机制的关键步骤是在Q(P)位点氧化底物喹啉时电子的分离，当铁硫蛋白（ISP）的外在结构域（ISP-ED）位于b位置时，两个电子同时转移至ISP和细胞色素b(L)。对bc(1)的预稳态快速动力学分析表明，还原态的ISP-ED只有在还原态的细胞色素b(L)被细胞色素b(H)氧化后才会移动到c(1)位置以还原细胞色素c(1)。然而，ISP-ED的构象转换是如何启动的问题仍未得到解答。在bc(1)复合物的各种氧化还原状态下，对两种类型的Q(P)位点抑制剂Pm和Pf的抑制效力和结合亲和力分析所获得的结果表明，从血红素b(L)到b(H)的电子转移是还原态的ISP-ED从b位置释放到c(1)位置以还原细胞色素c(1)的驱动力。
