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cellular retinol-binding protein 3 Cellular retinol-binding proteins (CRBPs) participate in the cellular uptake of vitamin A in the form of free retinol. Retinol achieves a higher chemical stability when bound to CRBPs, and its interaction with retinol-binding proteins allows the solubilization in the aqueous medium of the hydrophobic retinol molecule. There are four human CRBP types (CRBP1, -2, -3, -4) which differ in their tissue-specific expression pattern, as well as in their different ligand affinities. This group includes human CRBP3 (also known as retinol-binding protein 5, HRBPiso) which is expressed at highest levels in kidney and liver. CRBP3 binds retinol, and may be a human intracellular carrier of retinol in such tissues. CRBPs belong to the intracellular fatty acid-binding protein (FABP) family, members of which are small proteins that bind hydrophobic ligands in a non-covalent, reversible manner, and, besides CRBPS, include the cellular retinoic acid-binding proteins (CRABPs) and the fatty acid-binding proteins (FABPs). |
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