Properties of opsin-lipid complex in aqueous 2-chloroethanol

Cattle and squid opsins were found to be associated with phospholipids after extensive dialysis of the salt-free digitonin extract of rhodopsin against 30% aqueous 2-chloroethanol (v/v) at pH 2.5. The approximates sizes of opsin-lipid complexes were estimated by sedimentation studies to be around 110,000 and 150,000 daltons, respectively, for the cattle and the squid opsin. Phospholipids did not dissociate from opsin even in 80% 2-chloroethanol. The complexes were purified by passage through a Sephadex G-200 gel column equilibrated with 30% 2-chloroethanol. The optical properties of the complex suggested the presence of beta-conformation and a small amount of alpha-helix in solubilized cattle opsin.