Enzymes play an increasingly important role in many industrial fields such as food, feed, cosmetics and pharmacy. However, enzymes are susceptible to the external environment such as pH and temperature, and the practical operational conditions for enzymes are dramatically different from their physiological conditions, so most enzymes are not sufficiently stable and they are prone to lose their activity under practical operation. This has largely limited their wider industrial application. Currently, directed evolution, glycosylation and chemical modification have been extensively used to improve the enzyme stability, activity and expand the substrate scope. Among them, directed evolution, through which mutants bearing desired properties are obtained by gene diversification manipulation and library screening in vitro, has become a popular technique for enzyme modification. In practical application, medium engineering, immobilization and multi-enzyme complexes have been widely adopted to enhance the catalytic efficiency of enzyme. Among them, multi-enzyme complexes have gained special attention recently due to its substrate channeling effect which can significantly increase the reaction rate for cascade enzymatic reactions. The recent progress of enzyme application is introduced. Then, the popular techniques including directed evolution, glycosylation and chemical modification for the improvement of enzyme properties are reviewed. At last, the techniques including medium engineering, immobilization and multi-enzyme complex for the catalytic engineering of enzyme in practical application are summarized.

Contents
1 Introduction
2 Current application of enzymes
3 Enzyme modification
3.1 Directed evolution
3.2 Glycosylation
3.3 Chemical modification
4 Catalytic engineering of enzymes
4.1 Medium engineering
4.2 Immobilization
4.3 Multi-enzyme complex
5 Conclusion