Light-dark conformational states in bacteriorhodopsin

Abstract

Dark adapted or illuminated preparations of purple membrane fragments from Halobacteriumhalobium were treated with bifunctional crosslinking reagents. Glutaraldehyde (7.5 Å length) and dimethyl adipimidate (8.5 Å length) showed marked differences in their affect on proton pump activity when treated in the dark and under illumination, respectively; but there was no significant difference in activity after light-dark treatment in the case of dimethyl suberimidate (11.5 Å length). Net proton pump activity was also found to increase after imidoester treatment. The changes in proton pump activity seemed to have no direct correlation with the loss of free amino groups, but tryptophanyl residues seem involved. It is concluded that bacteriorhodopsin can exist in two chemically distinguishable conformational states in the dark and light, respectively.