Amino-acid sequence determination of a hydrophobic region of bovine rhodopsin.

The 50 amino acid residues sequence of a hydrophobic region of bovine rhodopsin, a membrane protein of retinal rod photoreceptors of molecular weight 39,000 was determined. This primary structure determination was performed on the S5 fragment (about 12,000 molecular weight) obtained from 2-(2 nitrophenylsulfenyl)-3-methyl-3'bromo-indolenine cleavage of the protein. Automatic Edman degradation used in liquid phase was performed in presence of N-cetyl-N,N,N-trimethyl-ammoniumbromide, a cationic detergent incorporated in the proteic film. S5 is a C-terminal rhodopsin fragment and contains the phosphorylation sites. The covalent structure determined overlaps with the sequence of an already known fragment [1]; thus 25 per cent of the rhodopsin primary structure is now elucidated. Our results are in agreement with and chiefly refine the topological model for rhodopsin which correlates its membrane location and its functional sites.