Reactions between alkyl phosphates and acetylcholinesterase from different species

Abstract

1. 1. There are considerable differences between acetylcholinesterase (AChE) from different species with regard to their reactions with organophosphorous anticholinesterases. AChE from chicken brain was inhibited 20 times as fast with 2-MPAM-ES as rat and mouse brain AChE. In contrast AChE from frog brain was inhibited 1000 times slower with 2-MPAM-ES, 100 times slower with DFP and 10 times slower with 2-MPA-ES than rat brain AChE. 2. 2. The differences in inhibition rates were similar for membrane-bound enzymes and enzymes solubilized by Triton X-100. 3. 3. Both chicken and frog brain AChE were inhibited to the same extent by quaternary ammonium salts. 4. 4. There were only small species differences with regard to reactivation of DFP-inhibited enzymes by 2-PAM. 5. 5. When AChE from the different species were inhibited by DFP, the enzyme from frog brain “aged” 10 times slower than in the other enzymes. 6. 6. Substrate specificity studies showed that chicken brain enzyme exhibited its highest activity towards propionylcholine whereas frog enzyme had the highest activity towards acetylcholine.