A model system for bacteriorhodopsin chromophore.

The absorption characteristics of bacteriorhodopsin chromophore cannot be understand on the basis of a simple protonated Schiff-base linkage. A possible hypothetical explanation may be an interaction of the aromatic amino acid residues also with retinal. Mixtures of retinal and tryptophan analogues were reacted in organic solvents. Many similarities were found in the absorption spectra of the different products of these reactions and in those of the main forms of bacteriorhodopsin photocycle. Such products are suggested to model the purple complex of bacteriorhodopsin as well as the chromophores of the photointermediates.