Resonance Raman studies of bovine metarhodopsin I and metarhodopsin II

Abstract
The resonance Raman spectra of bovine metarhodopsin I and metarhodopsin II were measured. The spectra were compared with model chromophore resonance Raman data. Metarhodopsin I was linked to opsin via a protonated Schiff base linkage; metarhodopsin II was linked by an unprotonated Schiff base. A recent suggestion that the chromophore of metarhodopsin II is retinal was explicitly disproved. The chromophores of both metarhodopsins had an essentially all-trans conformation. The basic mechanism for color regulation in both forms appeared to be electron delocalization. The data tended to support the model of cis-trans isomerization as the primary mechanism for vision. The conclusions and inferences of this work on energy uses and storage by rhodopsin in neural generation were discussed.