Kinetics and Quantitative Structure-Activity Relationships for Pseudomonas sp.Lipase-Catalyzed Hydrolysis of Both Monoesters and Diesters of Ethylene Glycol

摘要

The goal of this work is to study kinetics and quantitative structure-activity relationships for steady states of Pseudomonas sp.lipase-catalyzed hydrolysis of both diesters and monoesters of ethylene glycol.Based on the steady-state kinetics of the enzyme-catalyzed hydrolysis of the diesters of ethylene glycol,the diesters and the monoesters react simultaneously as soon as monoester has started to build up in the reaction medium.In other words,the apparent K_m values of the diesters are the K_m values of the diesters (K_(mA)) plus the K_m values of the monoesters (K_(mB)),and all V_(max) values are about the same.Moreover,the pH-stat titration curve of the enzyme-catalyzed hydrolysis of the diesters of ethylene glycol is initially hyperbolic,then there is a sharp falloff in the hydrolysis rate.The abrupt stoppage of the reaction (relaxation stage) may be due to the existence of two phases in the reaction medium,that is,the product (ethylene glycol) and the substrates (the diesters of ethylene glycol) are not miscible.Furthermore,quantitative structure-activity relationships for varied acyl groups of mono-and diesters of ethylene glycol are studied.The fact that both pK_(mA) and pK_(mB) values are linearly correlated with the hydrophobicity constant (pi) but not with the electronic substituent constants (sigma*) indicates that the affinity of these substrates for the enzyme depends only on the hydrophobicity of substrates.