Retinol receptors of the retina and pigment epithelium: Further characterization and species variation

Abstract

Cytosol (100 000 × g supernatant) fractions of retina, pigment epithelium, liver and brain and also serum samples of diverse animal species demonstrate discrete peaks of bound [ 3H]retinol as assessed by sucrose density gradient ultracentrifugation. Retina cytosol of rat, guinea pig and chick embryo demonstrates only a 2 S binding species (“receptor”) although bovine retina also has a much more rapidly sedimenting peak. Pigment epithelium and liver show 2 S and 5 S species while brain shows little 2 S binding. Saturation of specific binding sites and reversibility of [ 3H]retinol binding in chick retina cytosol are observed by both sucrose gradient and gel filtration analysis. Treatment with DNase, neuraminidase or lipase has little effect on retinol binding to the 2 S receptor. From this and a previous study Wiggert and Chader, 1975 we conclude that a limited number of retinol receptors are present in retina and other tissues which are protein in nature and which bind the vitamin with high affinity and specificity.