Transition from octahedral to tetrahedral geometry causes the activation or inhibition by Znf2+ of Pseudomonas aeruginosa phosphorylcholine phosphatase.

Pseudomonas aeruginosa phosphorylcholine phosphatase (PchP) catalyzes the hydrolysis of phosphorylcholine, which is produced by the action of hemolytic phospholipase C on phosphatidylcholine or sphyngomielin, to generate choline and inorganic phosphate. Among divalent cations, its activity is dependent on Mg(2+) or Zn(2+). Mg(2+) produced identical activation at pH 5.0 and 7.4, but Zn(2+) was an activator at pH 5.0 and became an inhibitor at pH 7.4. At this higher pH, very low concentrations of Zn(2+) inhibited enzymatic activity even in the presence of saturating Mg(2+) concentrations. Considering experimental and theoretical physicochemical calculations performed by different authors, we conclude that at pH 5.0, Mg(2+) and Zn(2+) are hexacoordinated in an octahedral arrangement in the PchP active site. At pH 7.4, Mg(2+) conserves the octahedral coordination maintaining enzymatic activity. The inhibition produced by Zn(2+) at 7.4 is interpreted as a change from octahedral to tetrahedral coordination geometry which is produced by hydrolysis of the [Zn(2+)L(2)(-1)L(2)(0) (H(2)O)(2)] complex.