FIG. 3.

(A) pH dependence of the PDE-A activity of YahA. (B) Dependence of the PDE-A activity of YahA on divalent metal cations. The PDE-A reaction buffer (pH 9.35) contained different divalent metal cations (final concentration, 5 mM) instead of Mg²⁺. The bar on the right shows inhibition of the PDE-A activity in the standard reaction buffer containing 5 mM (final concentration) MgCl₂ or 5 mM (final concentration) MnCl₂ by Ca²⁺ (5 mM [final concentration] CaCl₂). The reaction with Co²⁺ was carried out in PDE buffer at pH 8.4 to avoid precipitation of Co²⁺ complexes at higher pH values. The error bars indicate the standard deviations calculated from at least three replicates.