Reduction of extracellular dehydroascorbic acid by K562 cells.
K562 erythroleukaemic cells produced ascorbate when incubated with dehydroascorbic acid. The reduction depended on the number of cells and on the concentration of dehydroascorbic acid. The observed rate consists of a high affinity (apparent Km 7 mu M, Vmax 3 center dot 25 pmol min-1 (10(6) cells)-1 and a low affinity component, which was non-saturable up to 1 mM of DHA (rate increase of 0 center dot 1 pmol min-1 (10(6) cells)-1 (1 mu M of DHA-1). The rate was dependent on temperature and was stimulated by glucose and inhibited by phloretin, N-ethylmaleimide, parachloro-mercuribenzoate and the noyltrifluoroacetone. Although uptake of DHA proceeded at a higher rate than its extracellular reduction, the generation of extracellular ascorbate from DHA cannot be accounted for by intracellular reduction and the release of ascorbate, since the latter was not linear with time and had an initial rate of approximately 3 pmol min-1 (10(6) cells-1). At a concentration of DHA of 100 mu M this is 25 per cent of the observed reduction.
Department of Medical Chemistry, University of Vienna, Austria.
E
E
Schweinzer
Y
Y
Mao
P
P
Krajnik
N
N
Getoff
H
H
Goldenberg
D001205:Ascorbic Acid / Q000096:biosynthesis; D002614:Chelating Agents / Q000494:pharmacology; D002729:Chloromercuribenzoates / Q000494:pharmacology; D003683:Dehydroascorbic Acid / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005033:Ethylmaleimide / Q000494:pharmacology; D005609:Free Radicals / Q000037:antagonists & inhibitors; D006801:Humans; D004915:Leukemia, Erythroblastic, Acute; D007962:Leukocytes / Q000378:metabolism; D013804:Thenoyltrifluoroacetone / Q000494:pharmacology; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism; D020245:p-Chloromercuribenzoic Acid
D002614:Chelating Agents; D002729:Chloromercuribenzoates; D004791:Enzyme Inhibitors; D005609:Free Radicals; D013804:Thenoyltrifluoroacetone; D020245:p-Chloromercuribenzoic Acid; D005033:Ethylmaleimide; D001205:Ascorbic Acid; D003683:Dehydroascorbic Acid