Detergents for Extraction of Visual Pigments: Types, Solubilization, and Stability

This chapter discusses the detergents for extraction of types, solubilization, and stability of visual pigments. Visual pigments are intrinsic membrane proteins. They are insoluble in water; hence their characterization can only be accomplished with the aid of appropriate solubilizing agents, usually detergents. The choice of detergent is critically dependent on the needs of each individual investigator. Factors to be considered include detergent solubility, efficiency of membrane solubilization, visual pigment stability, regenerability, acceptable UV transmission, ease of removal, and defined chemical structure and purity. The majority of comparative studies on visual pigments from various species, however, have been carried out with digitonin. Commercial-quality digitonin usually precipitates in 1–2% aqueous solutions. The problem has been substantially overcome by isolating the soluble component, but this material has not been defined chemically. Although visual pigments are very stable in digitonin extracts, the agent is a very inefficient extractant.