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 degrees C, in 100 mM MOPS buffer (pH 8) containing 0.125 mM 5-5-dithio-bis(2-nitrobenzoic acid), 20-120 mu M acetylthiocholine and 0-20 mu M 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 mu M; alpha (competitive coefficient) = 5.8 +/- 2.0, 4.8 +/- 1.8 and 2.7 +/- 0.32; beta (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. (C) 2008 Elsevier Ireland Ltd. All Fights reserved.