What protein is required for retinol transport?

• A. Transferrin
• B. Albumin
• C. Ceruloplasmin
• D. Retinol-binding protein (RBP)

Answer: (D)

Retinol needs a dedicated carrier in the bloodstream to stay soluble and reach target tissues. Retinol-binding protein is the specific transporter for retinol in plasma, produced by the liver. It binds retinol to form holo-RBP, and this complex typically associates with transthyretin to prevent renal loss, ensuring efficient delivery to cells. The other proteins have different roles: transferrin transports iron; albumin is a general carrier for many substances but is not the primary retinol transporter; ceruloplasmin is a copper-containing enzyme involved in iron metabolism. So, the protein that specifically ferries retinol is retinol-binding protein.