Retinol binding protein Retinol-bindendes Protein;

Retinol ( vitamin A) is a fat-soluble vitamin which can only be transported in the blood plasma when it is bound to specific proteins. These binding proteins are called retinol-binding proteins, RBP for short.

There are four such specific binding proteins, which belong to the group of cytoplasmic lipid-binding proteins:

• CRBP I (from cellular retinol-binding protein)
• CRBP II
• CRABP I (from cellular retinoic acid binding protein)
• CRABP II

The four proteins consist of about 135 amino acids and have different tasks. Accordingly, they are also distributed differently in the different cells of the body. CRBP I promotes the conversion of retinol to retinylaldehyde or retinoic acid. It is mainly present in the pigment epithelial cells of the eye or the Kupffer star cells of the liver. CRBP II is necessary for the absorption of retinoids from the intestinal lumen and is found exclusively in the enterocytes of the small intestine. The exact function of the retinoic acid-binding proteins CRABP I and CRABP II is not clearly understood. CRABP I is present in most body cells, CRABP II on the other hand mainly in skin cells.