External Proton Uptake, Internal Proton Release and Internal pH Changes in Chromatophores from Rps. sphaeroides Following Single Turnover Flashes

Proton Translocation, Internal pH-Changes, Phosphorylation The change in internal pH in chromatophores from Rps. sphaeroides following short flash ex­ citation has been investigated using the method of the fluorescence quenching of 9-aminoacridine. (1) A single turnover flash induced a fluorescence quenching of ^ 0.4%. The fluorescence quenching was stimulated by valinomycin, and oligomycin, and inhibited by antim ycin A. (2) The extent of the pH gradient generated by a single turnover flash at the external pH ^ 8 was estimated to be less than 0.4 unit. (3) In a multiflash experiment the change in internal pH induced by each flash was found to be not linearly dependent on the number of protons which had been taken up after each flash from the external medium. We discuss the significance of the results with respect to the mechanism of phosphorylation. The release of H+ taken up outside the chromatophore into the membrane could not be excluded by the present results.