Monodehydroascorbate reductase activity in the surface membrane of leukemic cells. Characterization by a ferricyanide-driven redox cycle.
A transmembrane monodehydroascorbate reductase activity with a high affinity in the subpicomolar concentration range of the free radical can be measured at the surface of erythroleukemic cells using a ferricyanide-driven redox cycle. The activity is dependent on the membrane potential and can therefore only be found in intact cells. It is independent of the glutathione content of the cells. Thenoyltrifluoroacetone is an efficient inhibitor of the activity, whereas ouabain, monensin and tetraethylammonium show no effect. Cells are able to generate ascorbate from dehydroascorbic acid. This explains why both forms of vitamin C show practically the same affinity for the redox cycle but why it does not drive the redox cycle by itself because it is much slower and is not inhibited by thenoyltrifluoroacetone. The reductase activity is independent of the degree of differentiation of the leukemic cells.
Schweinzer
E
E
Department of Medical Chemistry, University of Vienna, Austria.
Goldenberg
H
H
D000818:Animals; D001205:Ascorbic Acid / Q000378:metabolism / Q000494:pharmacology*; D002454:Cell Differentiation / Q000187:drug effects; D002462:Cell Membrane / Q000201:enzymology; D003683:Dehydroascorbic Acid / Q000378:metabolism* / Q000494:pharmacology; D005292:Ferricyanides / Q000737:chemistry / Q000378:metabolism*; D006427:Hemin / Q000494:pharmacology; D007938:Leukemia / Q000201:enzymology* / Q000473:pathology; D008564:Membrane Potentials / Q000187:drug effects; D008985:Monensin / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism*; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D005292:Ferricyanides; D013757:Tetraethylammonium Compounds; C007931:hexacyanoferrate III; D010042:Ouabain; D019789:Tetraethylammonium; D006427:Hemin; D008985:Monensin; D010088:Oxidoreductases; C020666:glutathione dehydrogenase (ascorbate); D001205:Ascorbic Acid; D003683:Dehydroascorbic Acid