Stability, Toxicity, and Reaction Mechanism with Esterases of Certain Carbamate Insecticides

The stability, activity as inhibitors of acetyl- and butyrylcho-linesterase, and toxicity to house flies, Musca domestica L., and mice were compared for 30 N -alkyl and N,N -dialkylcarbamates. For each type of biological activity a distinctive structural specificity unrelated to stability was observed. The carbamates varied greatly in their inhibitory specificity for the acetyl- and butyrylcholinesterase and in the rate of attaining an equilibrium of cholinesterase, carbamate and acetyl choline during assay. Plasma albumin was found to hydrolyze p -Nitrophenyl N -alkylcarbamates rather than plasma cholinesterase or arylesterase. Chymotrypsin and human plasma butyrylcholinesterase did not react with the carbamates in a similar manner to their reaction with the acetates, ethyl carbonates and dialkyl phosphates derived from the same enols. These results indicate that competition rather than carbamoylation is the primary mechanism of cholinesterase inhibition and presumably toxicity for the N - alkyl and N,N -dialkylcarbamates studied.