Brandt U, Djafarzadeh-Andabili R
Universitätsklinikum Frankfurt, Zentrum der Biologischen Chemie, Frankfurt am Main, Germany.
Biochim Biophys Acta. 1997 Oct 20;1321(3):238-42. doi: 10.1016/s0005-2728(97)00060-1.
MOA-stilbene is a specific inhibitor of the ubihydroquinone oxidation center (center P or o) of cytochrome bc1 complex. Binding of this inhibitor does not require the 'Rieske' iron-sulfur protein, but is affected by the redox-state of the cytochrome bc1 complex. We have analyzed the pH dependence of the apparent dissociation constant for MOA-stilbene. A 2.5 fold change in affinity between pH 6.0 and 9.5 was observed for oxidized bovine cytochrome bc1 complex. The pH profile could be simulated by assuming a single protonable group with pKA = 7.7. This pKA was not observed after partial or complete reduction of the enzyme or after removal of the iron-sulfur protein. We conclude that this protonable group was identical to the redox-Bohr group with the same pKA that has been reported to be associated with the 'Rieske' iron-sulfur cluster. Fully reduced cytochrome bc1 complex exhibited an additional binding site for MOA-stilbene. As this second binding site was abolished by the center P inhibitor stigmatellin, but not by antimycin, an inhibitor of ubiquinone reduction at center N, we conclude that it is also located at center P.
MOA - 芪是细胞色素bc1复合物泛醌氧化中心（中心P或o）的特异性抑制剂。该抑制剂的结合不需要“里斯克”铁硫蛋白，但受细胞色素bc1复合物氧化还原状态的影响。我们分析了MOA - 芪表观解离常数的pH依赖性。对于氧化型牛细胞色素bc1复合物，在pH 6.0至9.5之间观察到亲和力有2.5倍的变化。通过假设一个pKA = 7.7的单一可质子化基团可以模拟pH曲线。在酶部分或完全还原后或去除铁硫蛋白后未观察到该pKA。我们得出结论，这个可质子化基团与具有相同pKA的氧化还原 - 玻尔基团相同，据报道该基团与“里斯克”铁硫簇相关。完全还原的细胞色素bc1复合物对MOA - 芪表现出额外的结合位点。由于这个第二个结合位点被中心P抑制剂柱晶白霉素消除，但未被抗霉素（中心N处泛醌还原的抑制剂）消除，我们得出结论它也位于中心P。
