Anticholinesterase effect of eserine (physostigmine) in fish and crustacean species

The kinetic characteristic (K-m) of cholinesterase from the crab Chasmagnat hus granulata, the shrimp Farfantepenaeus paulensis and the fish Odontesthe s bonaeriensis were compared and correlated with the anticholinesterasic ef fect of eserine (physostigmine). For the crustaceans, the estimated K-m val ues were about 5-8 times higher than that estimated for the fish (0.04 mM). In the crab and the shrimp, the concentration of eserine which inhibited 5 0% of cholinesterase activity (IC50) was estimated as 5.33x10(-4) and 4.33x 10(-4) mM,, respectively. In both cases, it was significantly higher (P < 0 .05) than that estimated for the fish larvae (7.43x10(-5) mM). A high K-m c ould reflect a lower affinity of the cholinesterase for its natural substra te, acetylcholine, or for substrate analogues such as carbamates and organo phosphorous pesticides. If we consider the IC50 for eserine as an index of enzyme susceptibility to pesticide inhibition, the cholinesterase from the fish larvae may be a better useful tool in assays for pesticide biomonitori ng than that from crustacean species.