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.