Modification Of Lipolase And Study Of Interfacial Catalysis Of Modified Enzyme

Lipases catalyze not only the hydrolysis of lipids in water but synthetic reactions in organic solvent, such as esterification and interesterification. The application of lipase for synthetic purpose has been under intensive study in recent years in the food, pharmaceutic cosmetics and so on. However, the stability and dispersibility of native lipase in organic solvent is much poorer than in water. It seems reasonable to attempt to prepare more stable enzymes in organic solvents to overcome its problems. Chemical modification as a rapid and inexpensive method can overcome problems above and improve its dissolution and catalysis property in organic solvent. The introduction of hydrophobic or amphoteric compounds onto the enzyme surface can promote dissolution into organic solvent through favorable interaction between these compounds and the solvent.In the paper, we introduce fatty acids onto the enzyme surface. The stearic acid was activated by N-hydroxysuccinimide. The lipolase was modified with activated stearic acid-hydroxysuccinimide ester through the reaction between the amino groups and activated fatty acids. The reaction was carried out at room temperature and in the case of the pH 7.4. The modification ratio can be controlled by changing the molar ratio and reaction time in the reaction system.The enzymatic activity, surface activity and interface behavior were studied. The hydrolysis activity, interfacial hydrolysis activity and esterification activity of the modified enzyme were assayed. The results showed that the interfacial hydrolysis activity at the interface of oil-water phase and esterification activity in hexane of the modified enzyme increased apparently, although the hydrolysis activity decreased little compared with the unmodified enzyme. After modification the surface activity of modified enzyme was improved. The surface tension and the interfacial tension of the modified and unmodified enzymes were also investigated. The surface tension and interfacial tension of the solution of modified enzyme was much lower than that of unmodified enzyme. The reduction in surface tension and interfacial tension is due to the adsorption of enzyme at two-phase interface. As enzyme adsorb to an interface, the reduction of surface/interfacial tension gives an indication of the characteristic adsorption.The Langmuir-Blodgtt monolayer film of modified enzyme was gained by use of LB technique and the surface pressure was higher than that of unmodified one, shown which was much more easer to congregate on interface. The AFM figure of modified enzyme showed a difference from that of unmodified enzyme. We can find the alkyl on the surface of the modified enzyme.From the above experimental results, it could be concluded that the lipolase modified with fatty acid had good behaviors in organic solvent and at interface of two-phase comparing to unmodified lipolase.