Hydrolysis of organophosphate esters: phosphotriesterase activity of metallo-beta-lactamase and its functional mimics.

The phosphotriesterase (PTE) activity of a series of binuclear and mononuclear zinc(II) complexes and metallo-beta-lactamase (mbetal) from Bacillus cereus was studied. The binuclear complex 1, which exhibits good mbetal activity, shows poor PTE activity. In contrast, complex 2, a poor mimic of mbetal, exhibits much higher activity than 1. The replacement of Cl(-) ligands by OH(-) is important for the high PTE activity of complex 2 because this complex does not show any catalytic activity in methanol. The natural enzyme mbetal from B. cereus is also found to be an inefficient catalyst in the hydrolysis of phosphotriesters. These observations indicate that the binding of beta-lactam substrates at the binuclear zinc(II) center is different from that of phosphotriesters. Furthermore, phosphodiesters, the products from the hydrolysis of triesters, significantly inhibit the PTE activity of mbetal and its functional mimics. Although the mononuclear complexes 3 and 4 exhibited significant mbetal activity, these complexes are found to be almost inactive in the hydrolysis of phosphotriesters. These observations indicate that the elimination of phosphodiesters from the reaction site is important for the PTE activity of zinc(II) complexes.