Temperature dependence and kinetic aspects of proton release and uptake by purple membrane

Abstract

Transient electric conductivity changes were detected on electric field aligned purple membrane suspension. The electric signal arises from the proton release and uptake by the purple membrane during the photocyle of bacteriorhodopsin. This electric signal contains several components. Two components can be distinguished with a short and a longer time delay similar to the fast and slow components of the M state. Both components contain proton release and uptake and were kinetically analysed; the temperature dependences of the rate constants were determined. In our interpretation the rate constants are related to the lifetimes of surface proton binding sites for release and uptake and the time delays to the inner proton movement inside the membrane. Two possible interpretations of the two components are discussed, one in connection with a sequential photocycle with back reactions, the other assuming two primary proton acceptors for the Schiff base.