BIOMOLECULES AND ENZYMES

Detailed explanation-1: -Vitamin A, retinol, circulates in blood bound to retinol binding protein (RBP). In some tissues, the retinol-RBP complex (holo-RBP) is recognized by a membrane receptor, termed STRA6, which mediates uptake of retinol into cells.

Detailed explanation-2: -Retinol is transported in blood bound to Aporetinol binding protein .

Detailed explanation-3: -To meet vitamin A requirements of tissues, the liver secretes retinol (vitamin A alcohol) into the circulation bound to its sole specific carrier protein, retinol-binding protein (RBP). The single known function of this protein is to transport retinol from the hepatic stores to target tissues.

Detailed explanation-4: -Cellular retinol-binding protein appears to have several roles, including (1) delivering retinol to specific binding sites within the nucleus and (2) participating in the transepithelial movement of retinol across certain blood-organ barriers.