Cytoplasmic-retinol binding protein

After entering the cell, retinol and retinoic acid (RA) are bound by separate cytoplasmic proteins. These cytosolic proteins are called cytoplasmic-retinol binding protein (CRBP) artd cytoplasmic retinoic acid-binding protein (CRABP). Two forms of CRBP exist, and tw o forms of CRABP exist. One form of CRiiP occurs mainly In the villi of the small intestines, while the other form occurs in the liver and other organs. One form of CRABP occurs in the skin, while the other form occurs in many tissues. 

Ottonello S, Petrucco S, Maraini G (1987) Vitamin A uptake from retinol-binding protein in a cell-free system from pigment epithelial cells of bovine retina retinol transfer from plasma retinol-binding protein to cytoplasmic retinol-binding protein with retinyl-ester formation as the intermediate step. J Biol Chem 262 3975-3981... 

Cell surfaces of body tissues appear to contain receptors for the retinol-binding protein. Many cells also contain cytoplasmic retinolbinding proteinss-u as well as proteins that bind retinoic acid.u-y These proteins are members of the large superfamily of hydro-phobic transporter molecules described in Box 21-A. This includes the milk protein 3-lactoglobulin, which also forms a complex with retinol.z,aa... 

Vitamin-E-binding sites have been demonstrated in a number of tissues. Catignani [240] has shown that the vitamin can bind to a cytoplasmic protein, with a molecular weight of about 31000, extracted from rat liver. Similar cytoplasmic proteins have been reported for 1,25-dihydroxycholecalciferol [241,242], retinol [243,244] and retinoic acid [245,246]. The vitamin-E-... 

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