RETINOID BINDING-PROTEINS REDIRECT RETINOID METABOLISM - BIOSYNTHESISAND METABOLISM OF RETINOIC ACID

Many tissues and cell types, starting early in embryogenesis, convert retinol (vitamin A) into an active form, all-trans-retinoic acid. This article will discuss a current model of retinol and retinoic acid met abolism that integrates the various reactions which maintain retinoic acid homeostasis, and will also integrate the enzymology with the func tions of cellular retinoid binding proteins. These conserved high-affi nity binding proteins enjoy widespread expression throughout all verte brates and throughout most vertebrate tissues. The binding proteins li mit access to retinol and retinoic acid to select enzymes and serve as substrates and affecters of retinoid metabolism.