Calibration and time resolution of lumenal pH-transients in chromatophores of Rhodobacter capsulatus following a single turnover flash of light: Proton release by the cytochrome bc1-complex is strongly electrogenic

Abstract

The flash-induced proton release into the lumen of chromatophores from Rhodobacter capsulatus was studied with Neutral red as pH-indicator. Calibration of the acidification jump after a single flash yielded a much larger figure, at least 0.8 units, than previously thought. A slow kinetic phase of proton release (85–90% of total) was sensitive to inhibitors of the cytochrome bc 1-complex. Its half-rise time, about 10 ms, was the same as the rise time of the electrogenic reaction in the cytochrome bc 1-complex that was recorded by electrochromism of carotenoids. The oxidoreduction of the two b-hemes was significantly faster ( t 1 2 ≅ 3 ms). Thus the major electrogenic event in the cytochome bc 1-complex is proton and not electron transfer.