Different states of aggregation for unbleached and bleached rhodopsin after isolation in two different detergents

Abstract

Phospholipid-free [bovine retina] rhodopsin was purified in the detergents sodium cholate and octaethylene glycol n-dodecyl (C12E8). In both detergents the native absorption spectrum of the unbleached protein is maintained; upon photolysis the preparation in C12E8 loses its ability to recombine with 11-cis-retinal, whereas the preparation in cholate does not. The circular dichroic spectra of the protein in the 2 detergents are nearly identical, indicating that the secondary structure of the protein is the same in the 2 detergents. The state of association of the protein in the 2 detergents is different. In sodium cholate the smallest species present was found to be a trimer of the rhodopsin polypeptide chain; this association was unaffected by exposure to light. In C12E8 the protein is monomeric and undergoes a nonspecific aggregation process on exposure to light. Apparently protein-protein interactions may play an important role in the stabilization of the native structure of rhodopsin.