Retinol-Binding Protein: The Serum Transport Protein for Vitamin A*

Publisher Website
Google Scholar
Abstract
Introduction THE transport of retinol (vitamin A alcohol) from retinoid (vitamin A and its analogs) stores in the liver to target tissues is accomplished exclusively by means of a specific transport protein, retinol-binding protein (RBP). RBP was first isolated in 1968 by Kanai et al. (1) and subsequently has been extensively studied in humans and rats. RBP is a single polypeptide chain with a molecular weight of about 21,000 and has one binding site for one molecule of all-trans retinol. In the blood, RBP circulates as a 1:1 molar complex with another serum protein, transthyretin (formerly called prealbumin). The formation of the RBP-transthyretin complex is thought to reduce the glomerular filtration and renal catabolism of RBP. Normal levels of RBP in human serum range between approximately 40 to 60 μg/ml. Within individuals, RBP levels are highly regulated and remain constant except in extremes of vitamin A nutriture or in disease. The topic of RBP was comprehensively reviewed by Goodman in 1984 (2). Since the publication of this review, much new information has become available concerning the chemical structure of RBP, the structure of the gene for RBP and its expression, hepatic synthesis and secretion of RBP, and the cellular uptake of retinol from RBP. The present review will focus primarily on the recent advances made in these areas. In addition, brief review of recent advances concerning some possible physiological roles of RBP will be given.

This publication has 0 references indexed in Scilit: