Inhibitors Directed Towards the Binuclear Metal Center of Phosphotriesterase

AbstractThe potential roles in binding and catalysis for the binuclear metal center found within bacterial phosphotriesterase were evaluated by characterization of the inhibitory properties of 26 substrate and product mimetics. Phosphonates bearing monofluoro, difluoro, or hydroxyl substituents at the methylene position were found to be noncompetitive inhibitors with Ki, values ranging from 0.6–9 mM versus the substrate paraoxon. Phosphoramidates did not significantly inhibit the enzyme. Diethyl phosphate and diethyl dithiophosphate inhibited the Cd-substituted enzyme with Ki values of 10 and 130 μM, respectively. The most effective inhibitor for either the cadmium or zinc substituted enzyme was found to be diethyl thiomethylphosphonate. The competitive inhibition constants for this compound were found to be 60 nM and 2.8 μM for the cadmium-and zinc-substituted enzyme, respectively. The tight binding is attributed to chelation of both metal ions simultaneously.