Irreversible inhibition of phosphorylase phosphatase by fluorophosphate.

The inactivation of phosphorylase phosphatase by fluorophosphate is described. The inactivation is dependent upon time and concentration of fluorophosphate and cannot be reversed by removal of fluorophosphate from the enzyme. Acid hydrolysis of fluorophosphate destroys the capacity for inhibition. The inactivation exhibits saturation kinetics. A dissociation constant for the enzyme-fluorophosphate complex and a rate constant for the reaction were calculated to be 5.5 × 10^?3 M and 0.22 min^?1, respectively. A competitive inhibitor, phosphate, protects the enzyme against inactivation. The data are consistent with an irreversible covalent modification of the active site of phosphorylase phosphatase by fluorophosphate.