NEUROTOXIC ESTERASE IN THE LAND SNAILS - INVITRO COMPARATIVE AND KINETIC-STUDIES

In vitro relative sensitivity of NTE of Helix aspersa and Theba pisana snails to eight organophosphorous compounds were investigated. The mo st potent inhibitors against NTE of H. aspersa snail were O-methyl O-2 ,5-dichlorophenyl phenylphosphonate and dimethoate-oxon with Ki values of 6.01 x 10(5) and 5.94 x 10(5) M-1 min-1, respectively. In the case of T. pisana, triphenyl phosphite and O-methyl O-2,5-dichlorophenyl p henyl-phosphonate showed high potency as NTE inhibitors with Ki values of 1.74 x 10(7) and 4.14 x 10(6) M-1 min-1, respectively. From the re sults obtained, NTE free of inhibitor had the highest dissociation con stant in both snails, where Km value of H. aspersa snail was 180 times smaller than Km value of T. pisana. The lowest Km value of H. aspersa snail was found to be 1.6 x 10(-3) M for EPN-oxon while the highest v alue was 1.2 x 10(-2) M for leptophos-oxon. On the other hand, the low est Km value of T. pisana snail did account for 2.4 x 10(-3) for dimet hoateoxon. Finally it could be concluded that ENP-oxon had the highest affinity to NTE of H. aspersa snail whereas leptophos-oxon had the hi ghest affinity to NTE of T. pisana snail.