Interaction between antimycin and cytochrome b_<560> in Chromatium chromatophores : The red shift of the absorption spectrum and photoreduction of cytochrome b_<560> in the presence of antimycin

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In the presence of dithionite, which reduced all the cytochromes present in Chromatium chromatophores, the addition of antimycin caused a shift (1-2 nm) of the a band in the absorption spectrum of reduced cytochrome b_<560> toward longer wavelength. The difference spectrum (antimycin-added-minus-no addition) had a trough at 556 nm, a peak at 564 nm and an isosbestic point at 561 nm. The locations of the trough, peak and isosbestic point did not depend on the concentration of antimycin, but the amount of shifted cytochrome b_<560> increased as the concentration of antimycin increased. As reported previously, a single-turnover flash reduced cytochrome b_<560> in the presence of antimycin. The extent of the reduction depended on the concentration of antimycin. Both titrations of the red shift and the photoreduction of cytochrome b_<560> with antimycin fitted a first-order sigmoid curve with a half-maximum value at 5 × 10^<-7> M of antimycin concentration. The results indicated that antimycin molecules interacted with, or were bound to, cytochrome b_<560> molecules in the ratio of one to one with an apparent dissociation constant of 3.5-7.3 × 10^<-7> M.
日本植物生理学会の論文