Cellular retinol-binding protein allows specific interaction of retinol with the nucleus in vitro

Purified cellular retinol-binding protein (CRBP), a potential mediator of vitamin A action, was found to enable retinol to bind in a specific manner to isolated nuclei from livers of vitamin A deficient rats. Binding was followed after complexing [3H]retinol with CRBP. The binding was specific, saturable, and temperature dependent. CRBP charged with unlabeled retinol or CRBP without retinol diminished binding of radioactivity whereas free retinol did not. No specific binding sites could be detected for free retinol. Purified cellular retinoic acid binding protein (CRABI) complexed with retinoic acid did not diminish the amount of retinol bound to nuclei. Approximately 3 x 10(5) specific binding sites per nucleus could be detected. Fewer binding sites were found in nuclei isolated from livers of control (chow-fed) rats and also from livers of vitamin A-deficient rats 2 hr after refeeding with retinylacetate.