Modeling the resonance Raman spectrum of a metarhodopsin: implications for the color of visual pigments.

Abstract

Resonance Raman spectra of an invertebrate rhodopsin are reported. The spectrum of squid [Loligo pealei] acid metarhodopsin is compared with the spectra of model compounds of the retinylidene chromophore in the all-trans conformation. Correlations made between acid metarhodopsin and these crystalline model compounds with known X-ray structures indicate that the chromophore in this intermediate is an all-trans protonated Schiff base. The data suggest a mechanism for the red shift in rhodopsin.