Affiliations: Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, OK 74078‐3035, USA | Howard Hughes Medical Institute and Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX 75235‐9050, USA
Abstract: The cytochrome bc_{1} complex from bovine heart mitochondria is a multi‐functional enzyme complex. In addition to electron and proton transfer activity, the complex also processes an activatable peptidase activity and a superoxide generating activity. The crystal structure of the complex exists as a closely interacting functional dimer. There are 13 transmembrane helices in each monomer, eight of which belong to cytochrome b, and five of which belong to cytochrome c_{1}, Rieske iron‐sulfur protein (ISP), subunits 7, 10 and 11, one each. The distances of 21 Å between b_\mathrm{L} heme and b_\mathrm{H} heme and of 27 Å between b_\mathrm{L} heme and the iron‐sulfur cluster (FeS), accommodate well the observed fast electron transfers between the involved redox centers. However, the distance of 31 Å between heme c_{1} and FeS, makes it difficult to explain the high electron transfer rate between them. 3D structural analyses of the bc_{1} complexes co‐crystallized with the Q_\mathrm{o} site inhibitors suggest that the extramembrane domain of the ISP may undergo substantial movement during the catalytic cycle of the complex. This suggestion is further supported by the decreased in the cytochrome bc_{1} complex activity and the increased in activation energy for mutants with increased rigidity in the neck region of ISP.
Keywords: Structure of cytochrome bc[TeX:] _1 complex, superoxide, ubiquinol‐cytochrome c reductase, mitochondrial processing peptidase
Journal: Biofactors, vol. 9, no. 2-4, pp. 103-109, 1999
