Fig. 2.

A) Inhibition of acetylthiocholine hydrolysis by the A-site inhibitor edrophonium or the P-site inhibitor propidium. Second order rate constants k_E were calculated from data in Fig. 3 of reference (6), and the ratios k_{E [I]=0}/k_{E +I} were fitted to eq. 3. For edrophonium, K_I = 0.31 ± 0.01 µM and α = 0.0034 ± 0.0014 (not significantly different from zero). Initial fitting with propidium gave α = −0.008 ± 004 (also not significantly different from zero), and α was fixed at 0 to give K_I = 1.61 ± 0.04 µM. B, C) Inhibitor competition assay for assignment of AChE binding site specificity. Values of k_E, with inhibitors I1 (thioflavin T) and I2 as indicated, were calculated from data in Fig. 3 of reference (6), and the ratios k_{E +I2}/k_{E [I2]=0} were fitted to the reciprocal form of eq. 4. K₂ values were set as the K_Is from Panel A, and K₁ for thioflavin T was fixed at 1.0 µM (6). For propidium and thioflavin T (panel B), the affinity in the binary complexes relative to that in the ternary complex was given by K₁₂/K₁ = 43 ± 8. For edrophonium and thioflavin T (panel C), K₁₂/K₁ = 0.81 ± 0.04. Dotted lines were calculated with the same values of K₁ and K₂ but with [I1]/K₁₂ fixed at 0.