Biochemistry of Visual Pigments

Bovine rhodopsin prepared by extraction from retinal outer segments with a nonionic detergent and chromatographic purification on calcium phosphate and ECTEOLA-cellulose migrated electrophoretically as a single band on polyacrylamide gel. The preparation showed spectral ratios of A400:A498 = 0.168 and A280:A498 = 1.75. By amino acid analysis the pigment gave a molecular weight of 28,000 per mole. The 190 and 276 mµ absorption of rhodopsin increased slightly on bleaching. Optical rotatory dispersion and circular dichroism measurements on the highly purified rhodopsin preparation indicate that native rhodopsin possesses approximately 60% helical structure and one-fifth of the helical content is lost on irreversible bleaching. The light-induced conformational change, however, is not observed with outer segments.