Cytochrome b_<560> in chromatophores from Chromatium vinosum

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A membrane-bound cytochrome of the B-type in Chromatium chromatophores, cytochrome b_<560>, was reduced both by flash light activation and continuous illumination in the presence of antimycin at controlled ambient redox potentials. The light-minus-dark difference spectra had peaks at 560 and 430 nm, and troughs at 445 and 415 nm. The reduction was observed in the ambient redox potential from 400 to about 200 mV. However, below 200 mV, a re-reduction of photooxidized C-type cytochrome superim-posed the reduction of cytochrome b_<560>. In the absence of antimycin, the reduction was not observed, suggesting that the reoxidation of cytochrome b_<560> was faster than the reduction. Dark titrations at various pH values showed that E_<m7> of the cytochrome b_<560> was about 40 mV and the E_m value was pH-dependent (-60 mV/pH) from pH 6 to 9. Cytochrome b_<560> had a pK at around pH 9. The content and some properties of cytochrome b_<560> were similar in chromatophores from either photoautotrophically or photoheterotrophically grown cells. The possibility of involvement of cytochrome b_<560> in the photosynthetic electron transfer is discussed.
日本植物生理学会の論文