Abstract: We had proposed external point-charge models to explain the variance in absorption maxima of cattle rhodopsin and the purple color of bacteriorhodopsin. In the former visual pigment model, a negative counteranion resides ca. 3 8, from the protonated Schiff base (SBH+) linkage and another point charge is located ca. 3 8, from C-12 and C-14 of the 11-cis-retinal chromophore (Figure la). In the bacteriorhodopsin model (Figure IC) a ...
