Inhibition of cholinesterase by epinephrine and norepinephrine.

Acetylcholinesterase and monoamine oxidase were found to be inhibited by each other's substrate. The inhibition of acetylcholinesterase by low concentration of epinephrine or norepinephrine was found to follow first-order reaction kinetics. The constants characterising this inhibition, the bimolecular rate ka (51.8 M-1 min-1 for epinephrine and 15.9 M-1 min-1 for norepinephrine) and the enzyme inhibitor dissociation constant (8.52 mM for epinephrine and 12.2 mM norepinephrine) were determined. The inhibition of acetylcholinesterase by epinephrine was found to be of the mixed type while its inhibition by norepinephrine was of the competitive type.