Illumination of bovine photoreceptor membranes causes phosphorylation of both bleached and unbleached rhodopsin molecules.

Bovine rod outer segments were given a series of flashes, each bleaching from 0.1% to 0.4% of the rhodopsin present. 9-cis-Retinal was then added, regenerating the bleaching pigment to isorhodopsin. The phosphorylated pigment species having either four and five or six and eight phosphates were isolated by chromatofocusing. The amounts of rhodopsin and isorhodopsin present in the phosphorylated species were determined spectrally. The species with four and five phosphates per rhodopsin were approximately 50% rhodopsin-50% isorhodopsin. The more highly phosphorylated species were almost entirely isorhodopsin. Presumably, the phosphorylated rhodopsin was phosphorylated without having been bleached. At a 4% bleach level, approximately 0.5 rhodopsin was phosphorylated with four to five phosphates for each rhodopsin that was bleached and phosphorylated.