Oxime Reactivation of Diethylphosphoryl Human Serum Cholinesterase

Reactivation of diethyl p-nitrophenyl phosphate inhibited human serum cholinesterase by pyridine-2-aldoxime methiodide and isonitrosoacetophenone has been investigated as a function of reactivator concentration, pH, and temperature in boric acid-borax buffer and in salt solution. Constants shown were the dissociation constants of the diethylphosphoryl cholinesterase reactivator complex for the reactivation by pyridine-2-aldoxime methiodide and the bimolecular rate constants for that by isonitrosoacetophenone. The protonation constants of the diethylphosphoryl cholinesterase were evaluated from the relationship between pH and the dissociation constants of the complex; they indicated a value of 8.4 in buffer medium and 7.8 in salt solution. Changes in reactivation rate and in apparent activation energy of reactivation due to the medium changes may be explained by the nature of the activated complex formed in the respective reactivation processes.