Inhibition kinetics of certain organophosphorus and carbamate pesticides on acetylcholinesterase from the snail Lymnaea acuminata.

k2, Kd and ki, for 2 organophosphorus (Phorate and Formothion) and 2 carbamate pesticides (Mexacarbate and Carbaryl) using acetylcholinesterase present in homogenates of the nervous tissue of the snail Lymnaea acuminata, were determined. Calculation of zero time velocities demonstrated that even in their P-S form the organophosphate compounds inhibited snail acetylcholinesterase. The kinetic constants of the 2 carbamates have been explained on the basis of their structure. The toxicity of the 4 pesticides has been explained on the basis of their kinetic constants.