RBP2 is an abundant protein present in the smallintestinal epithelium. It is thought to participate in the uptakeand/or intracellular metabolism of vitamin A. Vitamin A is afat-soluble vitamin necessary for growth, reproduction,differentiation of epithelial tissues, and vision. RBP2 may alsomodulate the supply of retinoic acid to the nuclei of endometrialcells during the menstrual cycle.