Ascorbic Acid Transport and Distribution in Human B Lymphocytes

Ascorbic acid (vitamin C) transport was investigated inhuman B lymphocytes. The vitamin was transported by two components. The first was a high-affinity activity with an apparent Km of 7-10 μM and Vmax of 0.14 mM/h (3.11 × 10−4 μmol × h−1 × mg protein−1). The activity was concentration and temperature dependent, saturable, and inhibited by carbonylcyanide-p-trifluoromethoxyphenylhydrazone and ouabain and generated ascorbic acid accumulation against a concentration gradient. Kinetics for the second component were indeterminate because ascorbate was not accumulated against a concentration gradient. Subcellular fractionation revealed that intracellular ascorbic acid in human B lymphocytes was >90% localized to the cytosol and not protein bound. Kinetic parameters of high-affinity ascorbic acid transport could operate effectively with plasma concentrations normally found in humans.