Inhibition of electric eel acetylcholinesterase by triarylmethane dyes

The effects of three cationic triarylmethane dyes - pararosaniline (PR), malachite green (MG), methyl green (MetG) - on electric eel AChE (eAChE) activity were tested at 25 °C, in 100 mM MOPS buffer (pH 8) containing 0.125 mM 5-5-dithio-bis(2-nitrobenzoic acid), 20-120 μM acetylthiocholine and 0-20 μM dye. All three dyes caused reversible, linear- or hyperbolic-mixed inhibition of esteratic activity. The respective inhibitory parameters for PR, MG and MetG were K_i = 8.4 ± 0.67, 1.9 ± 0.51 and 0.27 ± 0.017 μM; α (competitive coefficient) = 5.8 ± 2.0, 4.8 ± 1.8 and 2.7 ± 0.32; β (noncompetitive coefficient) = 0, 0 and 0.20 ± 0.011. The data were consistent with ligand binding at the peripheral site and a remote effect on substrate binding and turnover.