The enzyme catalyzed degradation of glycosidic linkage is one of the most important reactions in the nature with extensive applications to biomass conversion and pharmaceutical development.Traditionally,two possible mechanisms have been proposed to break the glycosidic bond,hydrolytic mechanism by glycoside hydrolases(GHs)and non-hydrolytic mechanism by polysaccharide lyases(PLs).In this work,we try to address different mechanisms for the cleavage of glycosidic bond using combined quantum mechanical and molecular mechanical method.It is believed that our simulations could provide detailed insights into our understanding of the enzymatic reactions.In particular,for the source of enzymatic catalysis enhancement,the possibilities of reactant destabilization,electronic resonance,and enzyme preorganization can be found in our simulations.