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 BC(1)-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) congruent to 3 ms). Thus the major electrogenic event in the cytochome bc(1)-complex is proton and not electron transfer.