Physicochemical Properties and Application Fields of Lysozyme

Lysozyme, also known as muramidase or N-acetyl murein hydrolase, is an alkaline enzyme that can hydrolyze glycosaminoglycans in bacteria. Lysozyme mainly breaks the β-1,4 glycosidic bond between N-acetylmuramic acid and N-acetylglucosamine in the cell wall to decompose the insoluble glycosaminoglycans in the cell wall into soluble glycopeptides, resulting in the release of the cell wall contents to dissolve the bacteria.

1. Physicochemical properties of lysozyme

The pure product of lysozyme is white, yellowish or yellow crystal or amorphous powder, no peculiar smell, slightly sweet, soluble in water, insoluble in acetone and ether. Lysozyme is easily destroyed by alkali, but in an acidic environment, lysozyme has strong thermal stability. When the pH value is 4-7, it can still maintain its activity at 100°C for 1 minute: the pH value is 3, it can withstand heat treatment at 100°C for 45 minutes.

The chemical properties of lysozyme are very stable, and its structure is almost unchanged when the pH value changes drastically within a certain range. The critical point of irreversible denaturation of lysozyme is 77°C. With the change of solvent, the critical point of irreversible denaturation also changes. When the pH value of the solution where lysozyme is in is less than 1, the critical point of irreversible denaturation decreases to 43°C. The optimal pH of lysozyme is 5.3~6.4, which can be used for antisepsis of low-acid food; as a preservative, lysozyme has high safety, can be frozen or dried, and has stable activity. The sensitivity of lysozyme to several denaturants was as follows: dioxane > dimethylacetamide > dimethylformamide > acetone, and it decreased linearly with the increase of solvent usage.

2. Application field of lysozyme

(1) Medical field

It can be used as a natural anti-infective substance with bactericidal effect. It has the effects of antibacterial, antiviral, hemostasis, swelling and pain relief, and accelerated tissue recovery. Lysozyme lozenges are used for acute and chronic pharyngitis, oral ulcers, etc.

(2) Food field

It has antibacterial effects on Gram-positive bacteria, aerobic spore-forming bacteria, Bacillus subtilis, Bacillus licheniformis, etc., but will not have adverse effects on human cells without cell walls. Therefore, it is suitable for the preservation of various foods. In addition, the enzyme can also kill intestinal spoilage bacteria, increase the anti-infection ability of the intestinal tract, and at the same time promote the proliferation of bifidobacteria in the intestinal tract of infants, and promote the digestion of milk casein curd, so it is also a good addictive for infant food and beverages. 

(3) Bioengineering field

The function of lysozyme to hydrolyze the bacterial cell wall helps to understand the structure of the bacterial cell wall: the protoplast prepared after the cell wall is decomposed can be used in academic research such as microbial classification and microbial breeding. In recent years, lysozyme has become an essential tool enzyme for cell engineering and genetic engineering, used to extract and manufacture enzymes, nucleic acids and active polypeptides.

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