Molecular characterization of two spontaneous antimycin A resistant mutants of Rhodospirillum rubrum.
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.
Uhrig
J F
JF
Lehrstuhl Biochemie der Pflanzen, Ruhr-Universität Bochum, Germany.
Jakobs
C U
CU
Majewski
C
C
Trebst
A
A
D000595:Amino Acid Sequence; D000968:Antimycin A / Q000494:pharmacology*; D001483:Base Sequence; D003573:Cytochrome b Group / Q000037:antagonists & inhibitors / Q000235:genetics; D004352:Drug Resistance, Microbial / Q000235:genetics*; D014450:Electron Transport Complex III / Q000037:antagonists & inhibitors / Q000235:genetics; D008689:Methacrylates; D008969:Molecular Sequence Data; D015363:Quinolones / Q000494:pharmacology; D012247:Rhodospirillum rubrum / Q000187:drug effects / Q000235:genetics*; D013844:Thiazoles / Q000494:pharmacology
D003573:Cytochrome b Group; D008689:Methacrylates; D015363:Quinolones; D013844:Thiazoles; C052097:aurachin D; C052096:aurachin C; D000968:Antimycin A; C030517:myxothiazol; D014450:Electron Transport Complex III