RESUMO
Vitamin C is a wide spectrum antioxidant essential for humans, which are unableto synthesize the vitamin and must obtain it from dietary sources. There are two biologicallyimportant forms of vitamin C, the reduced form, ascorbic acid, and the oxidizedform, dehydroascorbic acid. Vitamin C exerts most of its biological functionsintracellularly and is acquired by cells with the participation of specific membranetransporters. This is a central issue because even in those species capable of synthesizingvitamin C, synthesis is restricted to the liver (and pancreas) from which is distributedto the organism. Most cells express two different transporter systems for vitaminC; a transporter system with absolute specificity for ascorbic acid and a secondsystem that shows absolute specificity for dehydroascorbic acid. The dehydroascorbicacid transporters are members of the GLUT family of facilitative glucose transporters,of which at least three isoforms, GLUT1, GLUT3 and GLUT4, are dehydroascorbicacid transporters. Ascorbic acid is transported by the SVCT family ofsodium-coupled transporters, with two isoforms molecularly cloned, the transportersSVCT1 y SVCT2, that show different functional properties and differentialcell and tissue expression. In humans, the maintenance of a low daily requirement ofvitamin C is attained through an efficient system for the recycling of the vitamininvolving the two families of vitamin C transporters (AU)
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