33] Sulfhydryl chemistry of rhodopsin

Abstract

This chapter reviews the sulfhydryl chemistry of rhodopsin, followed by methodological directions for various relevant procedures. The data on the sulfhydryl chemistry of rhodopsin are almost exclusively restricted to the bovine species, because of the easy availability in large amounts. The six sulfhydryl groups of bovine rhodopsin exhibit clearly different reactivity/accessibility on treatment with SH reagents. These differences can be analyzed in great detail, as they are more or less dependent on certain conditions: (1) the type of reagent used; (2) the microenvironment of rhodopsin; and (3) whether or not the preparation is illuminated. This experimental versatility provides information on how the sulfhydryl chemistry of rhodopsin reflects its structural and functional integrity and allows important, though still tentative conclusions on the role of SH groups in structure and function of rhodopsin. It is evident that sulfhydryl modification studies on rhodopsin present a number of intriguing observations, which are, however, difficult to interpret unambiguously.