title: Alkali-induced reduction of the beta-cytochromes in purified complex III from beef heart mitochondria.
abstract: Approx. 40-50% of the cytochrome b in purified Complex III is reduced by ascorbate plus N,N,N',N'-tetramethyl-p-phenylenediamine or phenazine methosulfate at neutral pH. The remaining cytochrome b, including cytochrome b-565, is reduced by increasing the pH. The apparent pK for this reduction is between pH 10 and 11, and is more than two pH units higher than a similar alkali-induced transition in Mg-ATP particles. Alkali-induced reduction of cytochrome b occurs concomitantly with the exposure of hydrophobic tyrosine and tryptophan residues to a more hydrophilic environment. The relationship of these findings to the presence of a substrate accessibility barrier in Complex III is discussed.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001205:Ascorbic Acid / Q000494:pharmacology; D002417:Cattle; D003580:Cytochromes / Q000378:metabolism*; D004227:Dithionite / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000378:metabolism; D008773:Methylphenazonium Methosulfate / Q000494:pharmacology; D008931:Mitochondria, Muscle / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D013772:Tetramethylphenylenediamine / Q000494:pharmacology; D014364:Tryptophan; D014443:Tyrosine
chemical_list: D003580:Cytochromes; D004227:Dithionite; D008773:Methylphenazonium Methosulfate; D014443:Tyrosine; D014364:Tryptophan; D000255:Adenosine Triphosphate; D008274:Magnesium; D013772:Tetramethylphenylenediamine; D001205:Ascorbic Acid