Transition from octahedral to tetrahedral geometry causes the activation or inhibition by Zn super(2+) 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 super(2+) or Zn super(2+). Mg super(2+) produced identical activation at pH 5.0 and 7.4, but Zn super(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 super(2+) inhibited enzymatic activity even in the presence of saturating Mg super(2+) concentrations. Considering experimental and theoretical physicochemical calculations performed by different authors, we conclude that at pH 5.0, Mg super(2+) and Zn super(2+) are hexacoordinated in an octahedral arrangement in the PchP active site. At pH 7.4, Mg super(2+) conserves the octahedral coordination maintaining enzymatic activity. The inhibition produced by Zn super(2+) at 7.4 is interpreted as a change from octahedral to tetrahedral coordination geometry which is produced by hydrolysis of the $$ \left[ {{\text{Zn}}{ 2+ } {\text{L}}_{ 2}{ - 1} {\text{L}}_{ 2}{0} \left( {{\text{H}}_{ 2} {\text{O}}} \right)_{ 2} } \right] $$ complex.