| Chiral pesticides applied to environments can alter the activity and conformation of enzymes, consequently influence its function and physical metabolism. On the other hand, enzymes are involved in the enantioselective degradation of chiral pollutants including pesticides, resulting the relative enrichment of different isomers. Finally, the enzyme-catalyzed reaction of chiral compounds is an ideal system for researches on enzymatic mechanism and chiral conversion progress. Lipase (EC 3.1.1.3) exists extensively in the body of beings and soils. It is a significant hydrolysis enzyme and concerns with phenoxy acid ester herbicides and organophosphorus insecticides. Finally, lipases play important roles in asymmetric synthesis and chiral separation.On account of above reasons, the national product of Penicillium expansum alkaline lipase were chosen to study its interaction with chiral phenoxy acid herbicides, 2,4-DP, MCPP and 2,4-DPM. The effect of 2,4-DP, MCPP on lipase catalytic kinetics and the chiral hydrolysis of 2,4-DPM by lipase were studied detailedly. For the first time, we reported the enantioselective function of amino acid residues in lipase studied by chemical modification.Firstly the influence of 2,4-DP and MCPP on lipase catalytic kinetics was studied. The results showed that the inhibition was enantioselective. RS-2,4-DP in its high concentration obviously excited the lipase, but R-2,4-DP in its low concentration significantly inhibited the enzyme. In low concentration, 2,4-DP and MCPP both inhibited the lipase. While the inhibition of MCPP was stronger then 2,4-DP. The interaction between 2,4-DP with lipase was finished for a short period, it was affected slightly by incubated time. Similar effects were observed from the influence of MCPP on lipase.Using the chiral gas chromatography to monitor the residual ratio of enantiomers and their residual curves vs. time, it was confirmed that lipasecatalyzed chiral hydrolysis of 2,4-DPM. Due to the preferentially hydrolysis of S-2,4-DPM, R-2,4-DPM was enantioselective enriched in this reaction system. It was also reported that reaction temperature, pH value and the ratio of pesticide with lipase had effect on lipase enantioselectivity, respectively.The adsorption on kieselguhr enhanced the lipase enantioselectivity, expressed as ER value (enantiomer ratio), was increased from 1.58 to 5.31. It triggered changes in conformation of the enzyme by adsorption, thus lipase preferentially catalyzed S-2,4-DPM. It might be the major reason of enhanced enantioselectivity of enzymatic reaction. Also there was still no report on the influence of adsorption behavior on enzyme-catalyzed enantioselective hydrolysis chiral pesticides in environment.The investigation of environment factors on lipase enantioselectivity was carried out using soil components, calcium ion and amino acids. The results showed that kaolinite and calcium could enhance the lipase enantioselectivity. When kaolinite was applied into the reaction system, the lipase enantioselectivity achieved 8.33 from 1.35. While humic acid, L-arginine and L-glutamine had no effect on lipase enantioselectivity. L-tryptophan was found to decrease the ER value from 1.33 to 1.22. It was also observed that two particle-sizes of soil components could enhanced lipase enantioselectivity.For β-CDs, β-CD and CM-β-CD both decreased the enantioselectivity of enzymatic hydrolysis of 2,4-DPM, and the E value decreased from 1.30 to 1.26 and 1.12, respectively. But PM-β-CD did not alter the ER value of enzymatic hydrolysis.It was first reported here that enantioselective function of Cys, Arg, Trp, Lys and His residues in lipase was identified using chemical modification. It was concluded that the enzymatic catalysis and enzymatic enantioselective transformation might be different process, the amino acids involved could be same or different.
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