Kinetics of hydrolysis of acetylthiocholine and acetylcholine by cholinesterases.

Kinetics of hydrolysis of acetylthiocholine (ATCH) and acetylcholine (ACH) by butyrylcholinesterase (BCHE) and acetylcholinesterase (ACHE) are studied. ATCH is used for testing of enzymatic hydrolysis of ACH in vitro, because mechanism of ATCH hydrolysis is qualitatively similar to ACH and its reaction course can be quantitatively on-line measured by two independent methods: spectrophotometrical (determination of thiocholine - product of ATCH hydrolysis - using Ellman's method) and electrochemical (determination of acetic acid - product of ATCH hydrolysis - by pH-stat method). All tested hydrolyses correspond to the Michaelis-Menten's equation with the second irreversible step up to the total exhaustion of the substrate. The correlations were made by means of differential and integral kinetic equations describing Michaelis-Menten model. The optimal values of Michaelis constant (KM), maximum velocity (Vm), kinetic constants of single reaction steps and absolute concentration of the used enzyme were calculated for each experiment.