Erythrocytes reduce extracellular ascorbate free radicals using intracellular ascorbate as an electron donor.
Ascorbate is readily oxidized in aqueous solution by ascorbate oxidase. Ascorbate radicals are formed, which disproportionate to ascorbate and dehydroascorbic acid. Addition of erythrocytes with increasing intracellular ascorbate concentrations decreased the oxidation of ascorbate in a concentration-dependent manner. Concurrently, it was found, utilizing electron spin resonance spectroscopy, that extracellular ascorbate radical levels were decreased. Control experiments showed that these results could not be explained by leakage of ascorbate from the cells, inactivation of ascorbate oxidase, or oxygen depletion. Thus, this means that intracellular ascorbate is directly responsible for the decreased oxidation of extracellular ascorbate. Exposure of ascorbate-loaded erythrocytes to higher levels of extracellular ascorbate radicals resulted in the detection of intracellular ascorbate radicals. Moreover, efflux of dehydroascorbic acid was observed under these conditions. These data confirm the view that intracellular ascorbate donates electrons to extracellular ascorbate free radical via a plasma membrane redox system. Such a redox system enables the cells to effectively counteract oxidative processes and thereby prevent depletion of extracellular ascorbate.
VanDuijn
M M
MM
Department of Molecular Cell Biology, Sylvius Laboratory, Leiden University Medical Center, P. O. Box 9503, 2300 RA Leiden, The Netherlands.
Tijssen
K
K
VanSteveninck
J
J
Van Den Broek
P J
PJ
Van Der Zee
J
J
D001204:Ascorbate Oxidase / Q000378:metabolism; D001205:Ascorbic Acid / Q000097:blood*; D003683:Dehydroascorbic Acid / Q000031:analogs & derivatives* / Q000097:blood; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D004910:Erythrocyte Membrane / Q000378:metabolism; D004912:Erythrocytes / Q000378:metabolism*; D005609:Free Radicals / Q000097:blood; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D009243:NAD / Q000097:blood
D005609:Free Radicals; D009243:NAD; C000820:semidehydroascorbic acid; D001204:Ascorbate Oxidase; D001205:Ascorbic Acid; D003683:Dehydroascorbic Acid