Differences in salamander red cone and blue cone/green rod pigments

Abstract

Abstract: : Purpose:to compare and contrast pigment stability of salamander red cone and blue cone/green rod visual pigment proteins. Methods:Epitope tagged salamander visual pigment proteins were expressed in COS cells. Pigments were generated with 11–cis retinal or 11–cis 13–demethyl retinal analog and immunopurified in detergent (0.1% dodecyl maltoside). Pigment stability was assessed by monitoring pigment loss in a spectrophotometer as a function of time. Results: (1) The blue cone/green rod pigments remained intact in the dark over the course of 3 hours; whereas, the red cone pigment bleached in the dark with a time constant of about 90 min. (2) The presence of Cellular Retinaldehyde Binding Protein (CRALBP) had a small effect on blue cone/green rod pigment stability; whereas, CRALBP greatly accelerated red cone pigment loss in the dark 4–fold. (3) 13–demethyl retinal formed a pigment with the blue cone/green rod pigment with an absorption maximum identical to that of the wild–type pigment but with a significant decrease in pigment stability; a red cone pigment could not be purified with the same retinal analog. Conclusions: These results indicate that pigment stability can vary quite a bit between different cone pigment proteins. These differences might be directly related to the differences in red cone and green rod dark noise.

Keywords: color pigments and opsins • protein structure/function