Retinol Binding Protein

Retinol Binding Protein (RBP), a single-chain polypeptide glycoprotein, belongs to the a-globulin family of human plasma proteins and is the primary plasma transport protein for retinol (vitamin A1). RBP binds retinol in a 1:1 stoichiometry, serving not only to solubilize retinol but also to protect it from oxidation. Once in circulation, the RBP-retinol complex binds to one molecule of transthyretin (prealbumin), a plasma thyroxine-binding protein. This complex then delivers retinol to specific receptors of the retina, skin, gonads, lungs, salivary glands, and other tissues.

Immunoassays for serum levels of RBP are useful in the detection of liver disease, protein-calorie malnutrition, and vitamin A deficiencies. In addition, because vitamin A is important in the maintenance of differentiation and rate of proliferation of epithelial tissue, the determination of RBP serum levels have been shown to be important in the mediation of anti-tumor effects.