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Vitamin C transport systems of mammalian cells

Liang, Wei-Jun and Johnson, Daniel and Jarvis, Simon M. (2001) Vitamin C transport systems of mammalian cells. Molecular Membrane Biology, 18 (1). pp. 87-95. ISSN 0968-7688

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Official URL: http://dx.doi.org/10.1080/09687680110033774

Abstract

Vitamin C is essential for many enzymatic reactions and also acts as a free radical scavenger. Specific non-overlapping transport proteins mediate the transport of the oxidized form of vitamin C, dehydroascorbic acid, and the reduced form, Lascorbic acid, across biological membranes. Dehydroascorbic acid uptake is via the facilitated-diffusion glucose transporters, GLUT 1, 3 and 4, but under physiological conditions these transporters are unlikely to play a major role in the uptake of vitamin C due to the high concentrations of glucose that will effectively block influx. L-ascorbic acid enters cells via Na+-dependent systems, and two isoforms of these transporters (SVCT1 and SVCT2) have recently been cloned from humans and rats. Transport by both isoforms is stereospecific, with a pH optimum of ~ 7.5 and a Na+: ascorbic acid stoichiometry of 2 : 1. SVCT2 may exhibit a higher affinity for ascorbic acid than SVCT1 but with a lower maximum velocity. SVCT1 and SVCT2 are predicted to have 12 transmembrane domains, but they share no structural homology with other Na+ co-transporters. Potential sites for phosphorylation by protein kinase C exist on the cytoplasmic surface of both proteins, with an additional protein kinase A site in SVCT1. The two isoforms also differ in their tissue distribution: SVCT1 is present in epithelial tissues, whereas SVCT2 is present in most tissues with the exception of lung and skeletal muscle.

Item Type:Article
Additional Information:Online ISSN 0968-7688
Research Community:University of Westminster > Life Sciences, School of
ID Code:286
Deposited On:01 Dec 2005
Last Modified:12 Oct 2009 15:04

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