Comparative analysis of Syk kinase and protein Tyr phosphatase activities following diamide treatment. Erythrocyte membranes were treated with 0.1 mM diamide in the presence of increasing concentrations of GSH. Band 3 oxidation (percentage of maximal oxidation, in the absence of GSH) is showed in panel (a). Tyr kinase activity was measured as band 3 tyrosine phosphorylation at different diamide concentrations and expressed as percentage of maximal phosphorylation. PTP activity was measured as dephosphorylation of Tyr phosphorylated band 3 (obtained treating RBCs with 1 mM diamide) and expressed as percentage of maximal PTP activity (panel (b)). Band 3 oxidation and phosphorylation were quantified by Odyssey V3.0 software. Values are average of 3 separated experiments; the bars represent the standard deviations.