Laccase is a polyphenol oxidase containing four copper ions (p-bisphenol oxidase, EC188.8.131.52), belonging to the copper blue oxidase, in the form of monomer glycoprotein. Laccase exists in mushrooms, fungi and plants, and can also exist in the air. The only product after the reaction is water, so it is essentially an environmental-friendly antioxidant enzymes. Laccase has a wide range of applications in biological detection because of its unique catalytic properties. As an efficient biodetector, laccase has become an effective tool and means for the analysis of substrates, coenzymes, inhibitors and other components. Laccase has become the research object of many scholars in recent years because of the importance of environmental protection consciousness.
Laccase is the largest type of blue poly-copper oxidase, which has the catalytic properties of oxidizing polyphenols by comt and reducing oxygen to water. As early as 1883, Yoshida first discovered laccase in Japanese lacquer tree, becoming one of the earliest discovered enzymes in the world. Plant laccase has been neglected for a long time due to its lack of industrial application value. In the continuous development of biotechnologies such as removing polyphenols from industrial wastewater and lignin and pigments from textile printing and dyeing, laccase can oxidize polyphenols, lignin and other chemicals by using oxygen as an electron acceptor and produce the only by-product water. High quality conditions make the catalytic properties of laccase have wide application prospects in environmental protection, textile, printing and dyeing, food, chemical synthesis, and become one of the focus of scientific circles in the last decade. The research and development of new laccase, the space structure of laccase and its catalytic mechanism, the properties and application of laccase have become the focus of scientific research. Researchers in China have gradually realized the advantages of laccase in industrial applications, and the research momentum in recent years is swift and violent.
Large-scale industrialized production of microbial enzymes, which is a kind of whole cell biocatalysis and known as biotechnology or green chemistry, is one of the major areas of bio-economy advocated by Europe. Enzymes that can be used in industrial production must have some good properties, such as high temperature resistance, strong alkali resistance, resistance to shear force, and no inactivation during a certain storage period. The application range of fungal laccase is pH 4-6, temperature 30-50 C, and many substances are sensitive. Chloride, azide compound, hydroxide and so on can inhibit the activity of fungal laccase. In order to improve the properties of laccase and reduce the enzyme production cost, it is an effective method to express heterologous laccase by genetic engineering. However, because fungal laccase is a glycoprotein, and its glycosyl group has an important influence on the properties and activity of laccase, the heterologous expression of fungal laccase is difficult. Up to now, no successful expression of fungal laccase in E. coli has been reported.
In a word, laccase is a kind of polyphenol oxidase, because it is widely distributed in nature, and has a wide range of applications in environmental protection, textile, printing and dyeing, food, chemical synthesis and so on, in recent years has been widely concerned and studied.
Bacterial laccase can make up for the shortcomings of lipoxygenase, which generally does not have glycoprotein, and is easy to heterologous expression, genetic modification and large-scale fermentation production. The optimum pH for bacterial laccase is alkaline environment, high temperature resistance, and insensitive to inhibitors. As Wang reported, the half-life of laccase produced by Bacillus subtilis WD23 was 2.5 h at 80 C and 15 d at pH 9. A laccase was obtained from Bacillus C-125. The optimum pH of laccase was 7.5-8. Chloride did not inhibit laccase but stimulated laccase activity. Bacterial laccase shows great potential for application. But there are too few studies on bacterial laccase that seriously hamper the application of bacterial laccase. Therefore, it is of great significance to carry out extensive research on bacterial laccase.