Retinol Binding Protein (RBP4), Human Urine

Retinol binding protein (RBP4) is the specific carrier for retinol (vitamin A) in the blood. RBP4 delivers retinol from the liver to peripheral tissues. In plasma, RBP4 complexed with retinol interacts with transthyretin which prevents its loss by filtration through kidney glomeruli. RBP4 then transfers the retinol to other factors to facilitate retinol transport across the cell membrane.