Figure 6. Concentration-dependent inhibition of PTP activity in J774A.1 cell lysates by MPO-derived HOCl and HOSCN.

PTP activity in cell lysates (0.33±0.03 mg of cell protein/ml) was determined after incubation with 100 nM MPO, 100 mM Cl⁻ and increasing concentrations of SCN⁻ with 25 μM H₂O₂ for 15 min at 22 °C. Control samples contained cell lysates, MPO and H₂O₂ incubated under the same conditions, but in the absence of any added Cl⁻ or SCN⁻. After incubation MPO was removed before quantification of the released p-nitrophenolate anion as described in the legend to Figure 5. Values are means±S.D. of four determinations from two separate experiments. Statistical analyses were carried out using a repeated measures one-way ANOVA with Bonferroni's post-hoc test. *P<0.05 for the absence of both Cl⁻ and SCN⁻ compared with the presence of 100 mM Cl⁻. #P<0.05 for increasing concentrations of SCN⁻ in the presence of 100 mM Cl⁻ compared with the absence of SCN⁻.