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

The kinetic characteristic (Km) of cholinesterase from the crab Chasmagnathus granulata, the shrimp Farfantepenaeus paulensis and the fish Odontesthes bonaeriensis were compared and correlated with the anticholinesterasic effect of eserine (physostigmine). For the crustaceans, the estimated Km values 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 50% of cholinesterase activity (IC50) was estimated as 5.33x10-4 and 4.33x10-4 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 Km could reflect a lower affinity of the cholinesterase for its natural substrate, acetylcholine, or for substrate analogues such as carbamates and organophosphorous 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 biomonitoring than that from crustacean species.