Lysozyme

Lysozyme is 129 aminoacid residues enzyme (EC 3.2.1.17), hydrolase which catalyzes hydrolysis of 1,4-beta-linkages between N-acetylmuramic acid and N-acetyl-D-glucosamine residues in peptidoglycan and between N-acetyl-D-glucosamine residues in chitodextrins. Molecular weight of lysozyme is an approximately 14.7 kDa. Alternative name for lysozyme are 1,4-N-acetylmuramidase, L-7001, N,O-diacetylmuramidase, PR1-lysozyme, Globulin G1, Globulin G, Lysozyme G, Mucopeptide N-acetylmuramoylhydrolase, Mucopeptide glucohydrolase and Muramidase. This catalytic activity is non-specifically targeted to the bacterial cell membranes and related with general non-specific organism defence.

A bacteriolytic enzyme commonly found in nature and is present in almost all secreted body fluids and tissues of humans and animals. Lysozyme is present in chicken egg-white at high concentrations, accounting 3.5% of total egg white protein. It binds to ovomucin, transferrin or ovalbumin in egg white. Lysozyme is highly stable in acidic solution and heating at 100C for 1‐2 minutes. The thermal stability of lysozyme is partly due to its four disulfide bonds.

This enzyme is only effective against Gram positive bacterial cells. Gram negative bacteria and yeast are completely resistant to lysing by it.

In viruses (or bacteriophages), lysozyme is used as an agent to break into the host bacterial cell. Lysozyme from the tail of the virus (or bacteriophage) destroys the peptidoglycan bacterial cell wall and then virus can injects its DNA. After multiplication in bacteria, many lysozyme molecules are created to lyse the bacterial cell wall and release new viruses.

Functions

  • Exhibits therapeutic, antiviral and anti‐inflammatory properties
  • Induces the activity of phagocytizing cells
  • Influences immunological processes by stimulating immunoglobin synthesis
  • Promotes interferon synthesis and modulates tumour necrosis factor generation
  • Anti‐viral action by forming an insoluble complex with acidic viruses
  • Enhanced antibiotic effects
  • Anti‐inflammatory
  • Anti‐histaminic actions
  • Direct activation of immune cells
  • Anti‐tumour action

Uses

Pharmaceutical industry: against bacterial, viral or inflammatory diseases such as dental caries and spray for nasal tissue protection
Therapeutic creams: protection of the skin and soft tissues (e.g. burns, viral diseases).
Oral administration: shown to have an antihistaminic effect.
In cheese making: prevent off‐flavours and late blowing in some cheeses (e.g. Swiss Cheese, Parmesan, Edam, Gouda and Cheddar).
Acceleration of cheese ripening: lysis of starter bacteria releases cytoplasmic enzymes, which play a key role in proteolysis during cheese ripening
Brewing: control of lactic acid bacteria in beer. Sulfur dioxide (SO2) is commonly used to inhibit spoilage bacteria and yeasts in wines, but may cause allergic reactions in sensitive individuals. The high affinity binding of lysozyme to bacterial lipopolysaccharide results in reversible inactivation of its enzymatic activity

Why lysozyme has been used as an antimicrobial agent in various foods?

  • Heat stable
  • Active in a broad range of temperatures (from 1 C to nearly 100 C)
  • Withstands boiling for 1‐2 min
  • Stable in freeze‐drying and thermal drying
  • Not inactivated by solvents,
  • Maintains its activity when redissolved in water
  • Has optimum activity at pH 5.3 to 6.4 (i.e. typical for low‐acidic food)
  • The presence of other proteins in food, however, can reduce its stability by the formation of sulfide bridges

Related Links

Lysozyme in Wikipedia
http://lysozyme.co.uk/lysozyme-structure.php
Assay of lysozyme (EC 3.2.1.17)

English