Human cell dehydroascorbate reductase. Kinetic and functional properties.

Dehydroascorbate reductase (glutathione: dehydroascorbate oxidoreductase, EC 1.8.5.1) activity was examined in crude cytosol extracts of human cells. In blood neutrophil and lymphocyte extracts, the Km at pH 6.85 for dehydroascorbate was 1.3 mM, and for reduced glutathione 3.8 mM. Rates of dehydroascorbate uptake by intact human neutrophils, monocytes, lymphocytes and cultured fibroblasts were proportional to cytosol dehydroascorbate reductase activities. Dehydroascorbate reduction during dehydroascorbate uptake by these cells may be entirely enzymatic.