Proton uptake by light induced interaction between rhodopsin and G-protein

The light-induced proton uptake of rod outer segment disc membranes has been investigated in the absence and presence of G-protein. Proton uptake was measured as the alkalisation of the suspending medium using a pH electrode and/or the indicator dye bromocresol purple. It was found that besides the known proton uptake of photolysed rhodopsin additional uptake of one proton accompanies formation of the complex between rhodopsin and G-protein. No measurable proton uptake was found under conditions of rapid redissociation of the complex indicating an only transient protonation during its lifetime. Proton uptake was the same in washed membranes recombined with G-protein and in ordinarily stacked rod outer segments. The additional proton uptake reported here is not due to enhanced formation of the protonated photoproduct metarhodopsin II.