At 37 ℃ and in Tris-HCl buffer (pH＝7.4), enthalpy magnification technique and thermokinetic initial rate method were employed to study the hydrolysis reaction of acetylcholine bromide catalyzed by acetylcholinesterase (AchE) and the inhibition of the reaction by sodium dodecyl sulfate (SDS) under near physiological conditions. Molar enthalpy (ΔH_m,1) of the enzymatic reaction was determined to be 0.63 kJ•mol^－1 by deducting enthalpy of protonization of Tris base from total enthalpy of reaction system. Michaelis constant (K_m) and substrate inhibition constant (K_S) were also determined to be 0.85～0.94 mmol•L^－1 and 0.74～0.83 mmol•L^－1, respectively. SDS could remarkably decrease the rate of enzyme reaction but has less influence on biochemical constants of the enzyme. In SDS solution, inactivation rate of AchE follows first order reaction kinetics, the apparent first order inactivation constant is linear to action time and the fourth power of SDS concentration, and inactivation constant was calculated to be (2.47～2.69)×10¹³ mol^－4•L⁴•min^－1.

Key words: thermokinetics, acetylcholinesterase, acetylcholine bromide, sodium dodecyl sulfate, irreversible inhibition