Vitamin C transporters

Abstract

Vitamin C is a wide spectrum antioxidant essential for humans, which are unable to synthesize the vitamin and must obtain it from dietary sources. There are two biologically important forms of vitamin C, the reduced form, ascorbic acid, and the oxidized form, dehydroascorbic acid. Vitamin C exerts most of its biological functions intracellularly and is acquired by cells with the participation of specific membrane transporters. This is a central issue because even in those species capable of synthesizing vitamin C, synthesis is restricted to the liver (and pancreas) from which is distributed to the organism. Most cells express two different transporter systems for vitamin C; a transporter system with absolute specificity for ascorbic acid and a second system that shows absolute specificity for dehydroascorbic acid. The dehydroascorbic acid transporters are members of the GLUT family of facilitative glucose transporters, of which at least three isoforms, GLUT1, GLUT3 and GLUT4, are dehydroascorbic acid transporters. Ascorbic acid is transported by the SVCT family of sodium-coupled transporters, with two isoforms molecularly cloned, the transporters SVCT1 y SVCT2, that show different functional properties and differential cell and tissue expression. In humans, the maintenance of a low daily requirement of vitamin C is attained through an efficient system for the recycling of the vitamin involving the two families of vitamin C transporters.

Vitamin C in the Treatment and/or Prevention of Obesity

“…VC transport occurs by two main mechanisms: 1) VC enters the cells through a specific family of transporters (sodium vitamin C transporters 1 and 2) in a process mainly driven by sodium gradient (44) and 2) the oxidized form of VC, DHA, is transported inside the cell more rapidly than its reduced form, entering by facilitated diffusion through the 1, 3, and 4 isoforms of the glucose transporter GLUT (45)(46)(47). Once inside the cell, DHA is reduced to its original form, ascorbate.…”

Vitamin C and Disease: Insights from the Evolutionary Perspective

“…Uptake of glucose and DHAA also share the feature of insulin-dependency on the GLUT4 glucose transporter primarily found in muscle and adipose tissue [83]. In type 1 diabetes, deficiency of insulin has been shown to impair DHAA uptake of lymphoblasts [84].…”

Mutational Analysis and Modeling Reveal Functionally Critical Residues in Transmembrane Segments 1 and 3 of the UapA Transporter

“…At present, the function and specificity of nearly 20 NAT proteins are known. [1][2][3] These proteins come from bacteria, fungi, plants and mammals. All non-mammalian homologs of known function are specific for nucleobases; namely, xanthine, uric acid or uracil.…”