Vitamin A receptors. I. Comparison of retinol binding to serum retinol-binding protein and to tissue receptors in chick retina and pigment epithelium.

1. A simple, efficient three-step method for purification of serum retinol-binding-protein is described with homogeneity obtained after chromatography on DEAE-Sephadex, CM-Sephadex and Sephadex G-100. 2. Evidence is presented indicating that retinol receptors present in the cytosol fraction of chick retina and pigment epithelium are separate and distinct from purified retinol-binding protein. Fluorescence characteristics are different in tissue cytosol and serum as assessed by sucrose density gradient analysis. Tissue retinol receptors do not interact with human serum prealbumin although the prealbumin readily complexes with purified chicken retinol-binding protein. Likewise, no binding to serum retinol-binding protein antibody could be detected by sucrose density gradient analysis, in immunoprecipitation experiments or by double immunodiffusion. It thus appears that specific retinol receptors are present in neural retina and pigment epithelium that are different from serum retinol-binding protein.