PHOSPHOLIPID SOLUBILIZATION DURING DETERGENT EXTRACTION OF RHODOPSIN FROM PHOTORECEPTOR DISK MEMBRANES

The solubilization of rhodopsin and phospholipids from disks prepared from bovine retinal rods was studied using five different detergents. The relative amounts of rhodopsin and lipid extracted during membrane solubilization differed dramatically with the nature of the surfactant ; the two nonpolar detergents, Emulphogene (polyoxyethylene-10 tridecy lether) and octylglucoside, removed more protein than lipid; two bile salt-related detergents, 3-[(3-cholamidopropyl)dimethylammonio]-1-prop ane sulfonate (Chaps) and taurocholate, released relatively more lipid than protein; and digitonin, which shares characteristics with both g roups of detergents, extracted more lipid per mole of rhodopsin than t he former two but less than the latter two, Solubilization was tempera ture-dependent with all five detergents, though particularly so with o ctylglucoside: concentrations adequate for the total micellation of di sks at 23 degrees C were ineffectual at 4 degrees C, In total solubili zates of disks, the amount of lipid recovered in rhodopsin-lipid-deter gent micelles showed a closer correlation with the critical micellar c oncentration (CMC) than with the chemical nature of the detergent (oct ylglucoside > taurocholate > Chaps > digitonin > Emulphogene), The hig her the CMC, the larger the amount of lipid associated to the solubili zed rhodopsin and the larger the amount of lipid reassociated to rhodo psin upon surfactant dilution, For all five detergents, the lipid prog ressively extracted from disks during solubilization was relatively ri cher in phosphatidylcholine (PC) than the lipid in the original membra nes, The lipid which tended to be associated with rhodopsin in protein -lipid-detergent mixed micelles was also consistently richer in PC tha n that present in lipid-detergent micelles, Bleaching of solubilized r hodopsin decreased the amount of lipid in protein-lipid-detergent mice lles, Rhodopsin photolytic transitions were faster in nonionic than in bile salt-related detergents. (C) 1995 Academic Press, Inc.