The action mechanism of cellulase

The high catalytic efficiency and specificity of cellulase hydrolysis of cellulose have always been the most interesting problems.There is an active center in the detailed three-dimensional conformation of the enzyme macromolecule, located in a pit on the surface of the enzyme macromolecule.It first binds to the substrate (or complex), and then catalyzes hydrolysis, which can be divided into binding sites and catalytic sites.The binding site determines the enzyme specificity, and the catalytic site determines the enzyme activity and specificity.The shape and size of pit in the active center of enzyme preparation are different.

The hydrolysis reaction of cellulose by cellulase is a heterogeneous system, and its kinetics follows the (quasi-) first order reaction. Under the optimal temperature and pH conditions, the total reaction rate depends on the formation time of the complexes forming the enzyme first substance and the products.Although higher enzyme concentration can reduce the total reaction time, it is not desirable in practice.

The macromolecular structure of enzyme has many side groups of acidic and basic amino acids, which are in different dissociation states in different pH media. They will directly affect the binding and further reaction between enzyme and substrate, that is, the spatial conformation of enzyme macromolecule will affect its activity.Different types of enzymes have different state values for their optimal application.Therefore, different pH medium is needed when used, and the enzyme can be divided into three types: acidic cellulase, neutral cellulase and weakly alkaline cellulase.

The effect of treatment temperature on cellulase activity is complex, which can be roughly represented by a bell jar curve, that is, with the temperature increasing gradually, the possibility of the enzyme contacting the substrate increases, and the hydrolysis rate appears a maximum in a certain temperature range.If the temperature is increased further, the rate of hydrolysis decreases, which is thermally induced macromolecular inactivation (denaturation of proteins).Thus each enzyme has a narrow optimum temperature range.