Primary Photochemical Event in Bacteriorhodopsin: Study with Artificial Pigments

Artificial bacteriorhodopsin (bR) pigments based on synthetic retinal analogues with selectively blocked single and double bonds are prepared and submitted to pulsed laser photolysis. Similar experiments are carried out with short-chain aromatic analogues. It is concluded that only the C13=C14 double bond can be isomerized in the primary photoprocess. It is shown also that this process is accompanied by separation of the Schiff base from its protein counterion. The effective dielectric constant at the binding site and the nature of the Schiff base counterion play an important role in determining the absorption maximum of bR.