Enzymatic characterization of GST-ygiF PPPase activity.

(A) Enzyme activity as a function of PPP_i concentration. The curve was obtained by non-linear fitting to the Michaelis-Menten equation. The Mg²⁺ concentration was 5 mM. (B) PPPase activity as a function of pH at 0.5 mM Mg²⁺. (C) PPPase activity as a function of Mg²⁺ concentration. (D) Inhibition of PPPase activity by Ca²⁺ in the presence of Mg²⁺ (5 mM). If not otherwise stated, the substrate concentration was 0.5 mM and the incubation was carried out at 50°C and at pH 8.5. (Means ± SD, n = 3).