Interaction between antimycin and cytochrome b₅₆₀ in Chromatium chromatophores—The red shift of the absorption spectrum and photoreduction of cytochrome b₅₆₀ in the presence of antimycin
1980
Takamiya, Ken-ichiro
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 α 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 .
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