Occurrence of 11-cis-retinal-binding protein restricted to the retina

A binding protein for retinal (vitamin A aldehyde), the 11-cis-retinal-binding protein, was present in the soluble protein fraction of rat retina but was absent from brain, lung, heart, skeletal muscle, liver, kidney, spleen, small intestine, and testes. The binding protein was also found in human retina but not human liver. The binding protein for retinal from human retina did not bind retinol and was larger than, and readily separable from, the cellular retinol-binding protein which did not bind retinal. It would appear that the occurrence of a soluble binding protein for retinal, unlike the more widely distributed binding proteins for retinol and retinoic acid, may be unique to the retina.