Redox modulation of reductase and phosphatase activities in human erythrocytes

We have previously reported that ferricyanide reductase activity in human e rythrocytes depended on glycolysis and could be modulated by several compou nds including oxidants and hormones like insulin. Insulin could activate gl ycolysis, probably as a consequence of tyrosine phosphorylation of protein band 3, implicating phosphorylation reactions as an important signal for ac tivation of the reductase by insulin. Reversible phosphorylation of cellula r proteins is also believed to play a key role in the action of insulin. Cy tosolic acid phosphatase activity has been found in human erythrocytes. To further extend initial reports, we studied the effect of modulators on the cytosolic erythrocyte acid phosphatase. Mild oxidants like ferricyanide (1 mM), vanadate (1 mM), Mn2+ (0.5 and 1 mM), and phenylarsine oxide (10 and 1 00 mu M) inhibited the phosphatase activity. Similarly, insulin at concentr ations that stimulate ferricpanide reduction (500. 1000 mu IU/ml) inhibited the activity of the phosphatase enzyme. The overall results indicated that oxidants are able to inhibit the acid phosphatase and stimulate the redox enzyme. In addition, a significant negative correlation (r = -0.400; P = 0. 006) was observed between phosphatase and reductase activities. The observa tions discussed here, together with previous ones, emphasize that a close a ssociation between reductase and phosphatase enzymes may exist and also sug gest a role for redox reactions in tyrosine phosphorylation/dephosphorylati on-mediated signal transduction pathways.