Fig. (5) Effects of Mg²⁺ on Zn²⁺-activated hydrolysis of pNPP and bis-pNPP by CIAP. Reaction mixtures (200 µl) containing 25 mM Tris- HCl (pH 8.5), 2.5 mM p-nitrophenyl phosphate (A), or bis-p-nitrophenyl phosphate (B), 2 mM or 4 mM ZnCl₂ plus the indicated concentration of MgCl₂ (0-10 mM), and 10 µM CIAP were incubated at 37 °C for 10 minutes. Reactions were initiated by the addition of the substrate to the reaction mixture and stopped by the addition of 1.0 ml 0.5 M NaOH. Activities are expressed as change in A₄₁₀ per minute for phosphomonoesterase activity and change in A₄₁₀ per hour for the phosphodiesterase activity.