The reaction of human erythrocyte acetylcholinesterase (AChE) with a set of structurally related phosphoramidates was studied in order to investigate the properties of phosphorylated enzyme and the effects of 4 oximes PAM-2, TMB-4(Trimedoxime), HI-6 and BDB-106 on the reactivation of inhibited AChE. Second-order rate constant of the phosphorylation reaction of the compounds towards the active site of AChE range between 5.0 x 10(2) and 4.9 x 10(6) M-1min-1 and their inhibitory power (I50) was from 7.3 x 10(-5) to 5.7 x 10(-9) M for 20 min incubation at 37 degrees C. The oximes used were weak reactivators of inhibited AChE except for (C4H9O)(NH2)P(O)DCP (DCP, -O-2,5-dichlorphenyl group) and (C6H13O)(NH2)P(O)SCH3 where we have obtained good reactivation. Imidazole oxime BDB-106 proved to be a potent reactivator of tabun-inhibited AChE.
Title: Interaction of imidazolium and pyridinium dioximes with human erythrocyte acetylcholinesterase Franciskovic L, Spoljar MS, Reiner E Ref: Chemico-Biological Interactions, 87:323, 1993 : PubMed
Two pyridinium and two imidazolium dioximes were tested as reversible inhibitors of human erythrocyte acetylcholinesterase (AChE), as protectors of the enzyme against phosphorylation and as reactivators of the phosphorylated AChE. All four dioximes reversibly inhibited AChE, protected the enzyme against phosphorylation by soman and tabun and reactivated AChE after phosphorylation by sarin, VX and tabun. From the experimental results the enzyme/dioxime dissociation constants were evaluated for the catalytically active enzyme and for phosphorylated enzyme. The evaluation constants have shown that all four dioximes have about the same affinity for the catalytically active as for the phosphylated AChE. Obtained results also indicate that imidazolium dioximes probably bind only to the allosteric, while pyridinium dioximes bind to both, the catalytic and the allosteric site of the enzyme.
