Competition between retinal and 3-dehydroretinal for opsin in the regeneration of visual pigment

Rhodopsin regenerated faster than porphyropsin in all preparations of bullfrog opsin, bullfrog rod outer segment membrane and cattle opsin. When opsin was incubated with excess amount of an equimolar mixture of 11-cis-retinal and 11-cis-3-dehydroretinal, the composition of the regenerated pigment was simply dependent on the ratio of regeneration rates of rhodopsin and porphyropsin. This result can provide a mechanism to account for the discrepancy in vitamin A1/A2 composition between the retina and the pigment epithelium. The property of opsin preferring retinal to 3-dehydroretinal may be one of the basic factors affecting vitamin A1/A2 visual pigment systems.