Figure 4.

LpPPase enzymatic activity. (a) LpPPase enzymatic activity on p-nitrophenyl phosphate (pNPP) using Mg²⁺ as a metal cofactor. The curve was fitted with the Michaelis–Menten equation, which gave a K _m of 69.7 ± 18.8 mM and a V _max of 2.36 ± 0.27 nmol ml⁻¹ min⁻¹. (b) LpPPase activity was investigated with four alternative metal cofactors, Mn²⁺, Zn²⁺, Co²⁺ and Ca²⁺, using the pNPP concentration where V _max was previously reached. Inhibition by F⁻ in the presence of Mg²⁺ was also tested using sodium fluoride as a source of fluoride ions. The reaction velocities shown in (b) were normalized to V _max in (a), which was measured with Mg²⁺ as the metal cofactor. Error bars show standard deviations. Reactions were run in duplicate. n.d., not detected.