抄録
Bacteriorhodopsin is an only protein present in the purple membrane of a highly halophillic bacterium. The light energy which was absorbed in the retinal linked to the protein through the protonated Schiff base is used for proton ejection from the membrane and the subsequent uptake of proton from the opposite side of the membrane. In the present paper, the mechanism for the proton uptake was studied in terms of the changes in the electrostatic interaction among various protein residues and the Schiff base in the light-induced reaction process. The stabilization of the L' intermediate, whose decay is correlated with proton uptake, was governed by the pK_a=9 residue assigned to aspartic acid residue. The specific cationic residues, lysine and arginines, influenced the pK_a values of the aspartic acids and made the proton-donating system to the Schiff base active. A large UV spectral change associated with the formation of L' intermediate was revealed to be due to the unstacking of tryptophan residues from the retinal.
