Methodological and biological aspects to be considered in acetylcholinesterase reactivation assays using 2-PAM

Kinetic and toxicological characteristics of fish (Odontesthes argentinensi s) and crab (Callinectes sapidus) cholinesterases as well as methodological conditions to perform reactivation assays using pyridine 2-aldoxime (2-PAM ) were established. According to kinetic and eserine sensitivity data, both cholinesterases can be considered as acetylcholinesterases. The concentrat ion of eserine that inhibited 50% of enzyme activity (IC50) was estimated a s 15.9 x 10(-8) and 4.6 x 10(-8) M for crab and fish, respectively. For pur ified eel acetylcholinesterase (V-S type), it was estimated as 4.2 x 10(-8) M. 2-PAM showed both to increase non-enzymatic hydrolysis of acetylthiocho line iodide and to inhibit activity of the acetylcholinesterases tested. Th e IC50 of 2-PAM for crab acetylcholinesterase (8.2 x 10(-4) M) was signific antly higher than that from O. argentinensis (2.5 x 10-4 M) or eel (2.0 x 1 0(-4) M) acetylcholinesterase. Enzyme inhibition induced by 2-PAM showed to mask subtle inhibition due to malathion, suggesting that a previous charac terization of 2-PAM inhibition must be done before its use in reactivation assays. (C) 2000 Elsevier Science B.V. All rights reserved.