The Influence Of Solvent And Water Activity On Lipases' 1,3-positional Selectivity And Acyl-migration

Lipases with 1,3-positional selectivity play an important part in the synthesis of 1,3-diacylglycerol and oil modification. However, because of the existence of acyl-migration, the process is more complicated. It is important to systematically study the rule of 1,3-positional selectivity and acyl-migration, which would enrich the non-aqueous enzymatic theory and promote the application of 1,3-specific lipase in oil industry.Monoacylglycerol (MAG) was adopted as the model substrate for lipase's 1,3-positional selectivity study and the influence of solvents and water activity on the enzyme's 1,3-positional selectivity during lipase-catalyzed methanolysis of MAG was explored from the aspect of kinetics study for the first time. It was found that solvent greatly influenced 1,3-positional selectivity and acyl-migration in the process catalyzed by Lipozyme TL. As hydrophobicity increased, the 1,3-positional selectivity became weaker and so as acyl-migration; however, during the process catalyzed by Novozym 435, no 1,3-positional selectivity was observed. During the whole process, the acyl-migration rate decreased as hydrophobicity increased.The influence of water activity on the 1,3-positional selectivity and acyl-miragtion of the two lipases was examined extensively. The"Bell"plots of the enzymatic activity and positional selectivity were appeared with the increase of water activity. When water activity increased from 0.11 to 0.53, 1,3-positional selectivity became stronger in the process catalyzed by Lipozyme TL, however, when water activity increase from 0.53 to 0.97, 1,3-positional selectivity became weaker. And it was revealed that water activity had no remarkably effect on 1,3-positional selectivity catalyzed by Novozym 435. The rate of acyl-migration decreased as the water activity increased in both systems.Finally, triacylglycerol (TAG) was adopted as the model substrate for the study of the influence of solvents and water activity on the Lipozyem TL's 1,3-positional selectivity, and the mechanism was illustrated by the way of molecular Simulation.