Different Effects of Mg²⁺ and Zn²⁺ on the Two Sites for Alkylammonium Compounds in Pseudomonas aeruginosa Phosphorylcholine Phosphatase

Pseudomonas aeruginosa phosphorylcholine phosphatase (PchP) catalyzes the hydrolysis of phosphorylcholine (Pcho), is activated by Mg 2+ or Zn 2+ , and is inhibited by high concentrations of substrate. This study has shown that PchP contains two sites for alkylammonium compounds (AACs): one in the catalytic site near the metal ion-phosphoester pocket, and the other in an inhibitory site responsible for the binding of the alkylammonium moiety. The catalytic mechanism for the entry of Pcho in both sites and Zn 2+ or Mg 2+ follows a random sequential mechanism. However, Zn 2+ is more effective than Mg 2+ at alleviating the inhibition produced by the entry of Pcho or different AACs in the inhibitory site. We postulate that Zn 2+ induces a conformational change in the active center that is communicated to the inhibitory site, producing a compact or closed structure. In contrast, Mg 2+ produces a relaxed or open conformation.