Accumulation of Vitamin C (Ascorbate) and Its Oxidized Metabolite Dehydroascorbic Acid Occurs by Separate Mechanisms ()

It is unknown whether ascorbate alone (vitamin C), its oxidized metabolite dehydroascorbic acid alone, or both species are transported into human cells. This problem was addressed using specific assays for each compound, freshly synthesized pure dehydroascorbic acid, the specially synthesized analog...

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Bibliographic Details
Published in:The Journal of biological chemistry 1995-05, Vol.270 (21), p.12584-12592
Main Authors: Welch, Richard W., Wang, Yaohui, Crossman, Arthur, Park, Jae B., Kirk, Kenneth L., Levine, Mark
Format: Article
Language:English
Subjects:
Ascorbic Acid - analogs & derivatives
Ascorbic Acid - metabolism
Ascorbic Acid - pharmacology
Biological Transport, Active - drug effects
Dehydroascorbic Acid - chemical synthesis
Dehydroascorbic Acid - metabolism
Dithiothreitol - pharmacology
Fibroblasts - metabolism
Glucose - pharmacology
Humans
Kinetics
Male
Models, Chemical
Neutrophils - metabolism
Oxidation-Reduction
Sodium - pharmacology
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Summary:It is unknown whether ascorbate alone (vitamin C), its oxidized metabolite dehydroascorbic acid alone, or both species are transported into human cells. This problem was addressed using specific assays for each compound, freshly synthesized pure dehydroascorbic acid, the specially synthesized analog 6-chloroascorbate, and a new assay for 6-chloroascorbate. Ascorbate and dehydroascorbic acid were transported and accumulated distinctly; neither competed with the other. Ascorbate was accumulated as ascorbate by sodium-dependent carrier-mediated active transport. Dehydroascorbic acid transport and accumulation as ascorbate was at least 10-fold faster than ascorbate transport and was sodium-independent. Once transported, dehydroascorbic acid was immediately reduced intracellularly to ascorbate. The analog 6-chloroascorbate had no effect on dehydroascorbic acid transport but was a competitive inhibitor of ascorbate transport. The Ki for 6-chloroascorbate (2.9-4.4 μM) was similar to the Km for ascorbate transport (9.8-12.6 μM). 6-Chloroascorbate was itself transported and accumulated in fibroblasts by a sodium-dependent transporter. These data provide new information that ascorbate and dehydroascorbic acid are transported into human neutrophils and fibroblasts by two distinct mechanisms and that the compound available for intracellular utilization is ascorbate.
ISSN:0021-9258
1083-351X
DOI:10.1074/jbc.270.21.12584