2015 年 89 巻 5-6 号 p. 271-274
Vitamin A alcohol (retinol) binds to a family of proteins called retinol-binding proteins in order to neutralize hydrophobicity of the retinol. Plasma retinol-binding protein (RBP), which is also called RBP4 in recent classification, is an extracellular binding protein for retinol, and cellular retinol-binding protein (CRBP) I and II are intracellular binding proteins for retinol. These retinol-binding proteins also affect transport, storage and metabolism of vitamin A through various mechanisms. For example, retinol being transported in blood escapes renal excretion by binding to RBP and transthyretin. Another example is that retinol efflux and influx are regulated by stimulated by retinoic acid 6 (STRA6), a membrane receptor for RBP. Thirdly, enzymatic activities of intracellular retinol-esterifying enzymes, lecithin:retinol acyltransferase and acyl-CoA:retinol acyltransferase are modulated differently by CRBPs. The aspects of these phenomena are described based on the conformational findings of RBP and CRBPs.