On the ratio of the proton and photochemical cycles in bacteriorhodopsin.

The ratio of protons released per M-412 intermediate formed in illuminated purple membrane sheets of Halobacterium halobium varies from 0.3 to 3.0 as a function of the ionic strength and light intensity. The ratio increases with decreasing light intensity. At high ionic strength the illumination time affects the monophasic rate of proton uptake and biphasic rates of the M-412 decay. The influence of the ionic strength on the ratio is discussed on the basis of Gouy-Chapman theory as a consequence of pKa shifts of light-activated proton binding groups.