Effect of different ions on the specific activity of wild type Wzb. Reactions were carried out at 40°C with 2.5 mM pNPP as substrate in 50 mM MES – 50 mM HEPES, 1% BSA buffer, pH 8. Each ion was added at a final concentration of 0.1 mM. A. One ion was subtracted for each reaction type. B. Combinations of ions were added as indicated.