ABSTRACT
Bacteriorhodopsin (bR), a retinyl-protein closely related to visual pigments, is responsible for the photosynthetic activity of the purple membrane of the halophilic microorganism Halobacterium halobium. This chapter reviews work to clarify the molecular aspects of the function of bR and visual pigments using two main approaches. First is constructing synthetic retinal analogs bearing nonconjugated charges, as well as altering the retinal Schiff base environment, in order to evaluate the effects of electrostatic and solvation interactions on the retinal chromophore. Second is constructing artificial pigments based on synthetic retinals to provide insights into the chromophore-opsin interactions and their relevance to the absorption spectra of the pigments and their photoprocesses. Evidence that chromophore-opsin interactions affect the absorption maxima of bR has emerged from studies with artificial pigments derived from synthetic retinal analogs. The chapter discusses the opsin shift of bovine rhodopsin after considering the vibrational data for protonated retinal Schiff base and retinal pigments.
