Zhang Z, Huang L, Shulmeister V M, Chi Y I, Kim K K, Hung L W, Crofts A R, Berry E A, Kim S H
E. O. Lawrence Berkeley National Laboratory, University of California, 94720, USA.
Nature. 1998 Apr 16;392(6677):677-84. doi: 10.1038/33612.
The cytochrome bc1 is one of the three major respiratory enzyme complexes residing in the inner mitochondrial membrane. Cytochrome bc1 transfers electrons from ubiquinol to cytochrome c and uses the energy thus released to form an electrochemical gradient across the inner membrane. Our X-ray crystal structures of the complex from chicken, cow and rabbit in both the presence and absence of inhibitors of quinone oxidation, reveal two different locations for the extrinsic domain of one component of the enzyme, an iron-sulphur protein. One location is close enough to the supposed quinol oxidation site to allow reduction of the Fe-S protein by ubiquinol. The other site is close enough to cytochrome c1 to allow oxidation of the Fe-S protein by the cytochrome. As neither location will allow both reactions to proceed at a suitable rate, the reaction mechanism must involve movement of the extrinsic domain of the Fe-S component in order to shuttle electrons from ubiquinol to cytochrome c1. Such a mechanism has not previously been observed in redox protein complexes.
细胞色素bc1是位于线粒体内膜的三种主要呼吸酶复合物之一。细胞色素bc1将电子从泛醇转移至细胞色素c，并利用由此释放的能量在内膜上形成电化学梯度。我们对来自鸡、牛和兔的该复合物在存在和不存在醌氧化抑制剂情况下的X射线晶体结构进行研究，发现该酶的一个组分（一种铁硫蛋白）的外在结构域存在两个不同位置。一个位置距离假定的泛醇氧化位点足够近，使得泛醇能够还原铁硫蛋白。另一个位置距离细胞色素c1足够近，使得细胞色素能够氧化铁硫蛋白。由于这两个位置都无法使两个反应以合适的速率进行，因此反应机制必定涉及铁硫组分外在结构域的移动，以便将电子从泛醇穿梭至细胞色素c1。此前在氧化还原蛋白复合物中尚未观察到这样的机制。
