THE CIRCULAR DICHROISM OF SODIUM CHOLATE SOLUBILIZED RHODOPSIN

Abstract— The near UV and visible circular dichroism (CD) spectra of rhodopsin solubilized and purified in sodium cholate have been determined. The CD properties of rhodopsin in 2 and 20mg/ml sodium cholate are substantially different in terms of the α band to β band ratio, and sensitivity of the near UV CD spectra to bleaching. Rhodopsin in 2mg/m l sodium cholate will regenerate (11- cis -retinal + opsin → rhodopsin) and has a CD spectrum similar to rhodopsin in rod outer segment membranes and digitonin which will also regenerate. On the other hand rhodopsin in 20mg/m l sodium cholate will not regenerate and has CD properties similar to other nonregenerable detergents (cetyltri-methylammonium salts and emulphogene). These results indicate that CD reflects the conformational integrity of functional (regenerable) rhodopsin and that sodium cholate can reversibly alter the conformation of rhodopsin. Finally the results further support the validity of using sodium cholate solubilized rhodopsin as a model system for studies on the structure and function of rhodopsin.