Jaganathan_1998_Indian.J.Biochem.Biophys_35_142

The effect of non-ionic detergents like Triton X-100, Lubrol PX, Brij 35 and Tween 80 on the esterase activity and inhibitor sensitivity of human serum butyrylcholinesterase (BCHE) were studied. The results showed that though BCHE is not a detergent dependent enzyme, the esterase activity and inhibitor sensitivity of it can be modulated by the presence of detergents. All the detergents caused a marginal activation of the esterase activity. The presence of Lubrol PX, Brij 35 or Tween 80 did not affect the 50% molar inhibition concentration (IC50) of the inhibitors tested. But in the presence of Triton X-100 the IC50 values were increased for neostigmine, eserine and tetraisopropylpyrophosphoramide (acylation site interacting inhibitors), whereas for inhibitors like ethopropazine, imipramine and procainamide (choline binding pocket specific inhibitors) the IC50 values were unaltered. In addition, in the presence of Triton X-100 the bimolecular reaction constant for phosphorylation reaction (ki) of BCHE for the acyl pocket specific tetraisopropylpyrophosphoramide was reduced. Triton X-100 partially protected BCHE against this tetraisopropylpyrophosphoramide inactivation. These results indicate that Triton X-100 by interacting with the acyl pocket hydrophobic region is able to activate the esterase activity of BCHE. Further it reduces the capacity of the enzyme to react with inhibitors that inactivate it by interacting with the serine residue of the acylation site.