Cleavage of β-Carotene to Retinal

Abstract

Elucidating the physiological roles played by vitamins has always been a major goal of nutritionists and biochemists. In humans, vitamin A deficiency disorder (VADD) in milder forms leads to night blindness, whilst more severe progression can lead to corneal malformations, e.g. xerophthalmia (See Volume 5, Chapters 8 and 9 ). This deficiency also affects the immune system, leads to infertility and causes malformations during embryogenesis. The molecular basis for these diverse effects lies in the dual role of vitamin A (retinol, 1 ) derivatives. In all visual systems, retinal ( 2 ), or a closely related compound such as 3-hydroxyretinal ( 3 ), is the chromophore of the visual pigments ( e.g. rhodopsin) [ 1 , 2 ]. In vertebrates, the derivative retinoic acid (RA, 4 ) is a major signalling molecule that controls a wide range of processes. Retinoic acid is the ligand of the nuclear retinoic acid receptors (RARs) and retinoid X receptors (RXRs) [ 3 – 6 ] (see Chapter 15 ).