Kinetics of the blue light-induced inhibition of photoelectric activity of bacteriorhodopsin

Abstract

1. Introduction In previous photoelectron studies of bimolecular lipid membranes containing bacteriorhodopsin mem- brane sheets (BR) it was found that if this system is illuminated by green and blue light simultaneously, the latter is capable of decreasing the photopotential generated by green light [l] . It was proposed that the blue light induces fast conversion of BR412+BR570 in a fashion which is not coupled with proton pumping. A kinetic model of this effect has been elaborated [2] . The study of photoelectric activity of BR incor- porated into lipid-impregnated collodion film has revealed three electrogenic phases differing in time constants [3] On the basis of flash-photolysis absorp- tion measurements on BR water suspension, these phases were correlated with different steps in the photochemical cycle of BR. According to the com- parison of the kinetic parameters, simultaneously with the formation of BRaI a rise in the photo- potential indicates proton translocation from the Schiff-base in the pigment-protein complex. A further, slower rise in the photopotential following the regeneration of BR570 is due to the proton uptake from the opposite side of the membrane. The present paper deals with fast kinetic aspects of the blue light-induced decrease of the photopotential in connection with the BR photochemical cycle. The quenching was induced by a blue flash, following a green one, after appropriate delay times. It has been