Inhibition of cholinesterases by the zwitterionic detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS)

Abstract

3-[(3-Cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS), a zwitterionic detergent, behaves as a reversible inhibitor of several cholinesterases. Human and horse serum cholinesterases were more sensitive to inhibition by the detergent than the enzyme from Electrophorus electricus or human erythrocyte. Thus, CHAPS binds with butyrylcholinesterase in preference to acetylcholinesterase. Noncompetitive inhibition kinetics were observed with all enzymes tested; the apparent inhibition constants were 0.4, 2.5, 5.8, and 7.5 m m for the cholinesterases from human serum, horse serum, Electrophorus electricus, and human erythrocyte, respectively. The rate of phosphorylation of the cholinesterases by diisopropyl phosphorofluoridate was significantly reduced in assays performed in the presence of CHAPS; however, the detergent was unable to fully protect the cholinesterases from the inactivation by the organophosphate. These results indicate that the detergent binds in a noncompetitive manner to cholinesterases and this reduces the capacity of the enzymes to react with both the substrate and the organophosphate.