Vitamin A receptors: II. Characteristics of retinol binding in chick retina and pigment epithelium

Gel filtration studies demonstrate that retinol receptors of chick retinal and pigment epithelial cytosols are (1) of very similar nature (2) of small molecular size (about 18 000 daltons) and are different in character from serum proteins. Citral inhibits the binding of ³H] retinol to the retinal 2 S receptor. Retinol acetate competes with retinol for binding to 2 S receptor in both retina and pigment epithelium whereas retinol palmitate is an effective competitor only in the pigment epithelium. Dithiothreitol maximizes 2 S binding in retina and pigment epithelial cytosol; its absence does not lead to receptor aggregation however. A limited number of high affinity binding sites (2 S receptor) appear to be present in retina and pigment epithelium. A 5 S binding species is also present in pigment epithelium; it is similar in character to ³H] retinol binding in serum and may arise from serum contamination of the pigment epithelial preparation. Binding affinity in retina is high with possibly two classes of retinol binding sites present of K_D about 1·10^?9 and 4·10^?8.