Ascorbic acid inhibits protein tyrosine phosphatases in NIH 3T3 cells expressing human epidermal growth factor receptors.

1. Physiological concentrations of ascorbic acid inhibited PTPase activity in HER 14 cells. 2. Higher concentrations of ascorbic acid produced a weaker inhibitory effect on PTPase activity in HER 14 cells. 3. EGF prevented the inhibitory effect of ascorbic acid on PTPase activity in HER 14 cells. 4. The inhibitory effect of physiological concentrations of ascorbic acid on PTPase activity depends on density of the cell culture, with less dense populations exhibiting greater inhibition of PTPase activity. 5. These observations suggest that ascorbic acid might have a modulatory role in cellular phosphorylation-dephosphorylation events.