Uhrig J F, Jakobs C U, Majewski C, Trebst A
Lehrstuhl Biochemie der Pflanzen, Ruhr-Universität Bochum, Germany.
Biochim Biophys Acta. 1994 Sep 27;1187(3):347-53. doi: 10.1016/0005-2728(94)90008-6.
Antimycin A is an inhibitor of cytochrome bc1 complexes acting at the quinone reducing site (Qi) of the cytochrome b subunit. We report here the isolation and molecular characterization of two spontaneous mutants of the purple non-sulfur bacterium Rhodospirillum rubrum resistant to this inhibitor. In the two mutants antimycin A resistance was found to be conferred by replacement of an aspartate residue at position 243 of the cytochrome b polypeptide chain, in one case by histidine and in the other by glutamate. The mutants exhibit cross-resistance to aurachin C but not to aurachin D. The exchange of Asp-243 does not only diminish the antimycin sensitivity of the isolated cytochrome bc1 complexes but also has effects on the function of the quinone reducing site (Qi). Oxidant-induced reduction of cytochrome b, requiring addition of antimycin A in the wild type, is already at a maximum in the absence of antimycin A. This indicates a diminished electron flow between heme b-566 and ubiquinone at the quinone reducing site (Qi) of cytochrome b.
