An investigation of the in vitro inhibition of acetylcholinesterase by the carbamate inhibitor eserine sulphate in eserine resistant strains of Drosophila melanogaster

1. The kinetics of inhibition of AChE by the carbamate inhibitor eserine sulphate were investigated in five resistant strains of Drosophila melanogaster. 2. The dissociation constant (Kd) was higher and the carbamylation constant was lower relative to the control in four of these. 3. No change was observed in the decarbamylation constants (k3) of the five strains. 4. The Vmax of AChE was higher in the five resistant stocks than in the Canton-S/TM2 controls but no change in the Km of AChE for acetylthiocholine was observed. No electrophoretic variants of AChE were detected. 5. No increase in the activity of nonspecific esterases was detected in the resistant lines. 6. These results indicate that resistance to eserine sulphate may occur in D. melanogaster by a reduction in affinity of AChE for the inhibitor.