Lysozymes are lytic enzymes that hydrolyse glycosidic bonds and are widely distributed in nature. They are categorised into five classes. Hen egg‐white lysozyme is the best characterised of all proteins and its reaction mechanism is explained in detail. As well as serving as a model protein for studying structure and function of proteins, its antibacterial, antiphlogistic and immune functional properties are exploited in medicines and food additives. Basic concepts of enzyme reaction mechanism, structure and function, protein chemistry and stability are described. Evolution and diversity in structure as well as the function of lysozyme as a digestive enzyme are also discussed. Methodologies in studying proteins are described in detail. A recent debate on the reaction mechanism of hen egg‐white lysozyme is also reviewed.

Key Concepts

  • Lysozyme is the first enzyme whose 3D structure was elucidated with X‐ray analysis and is the best‐characterised protein.
  • The ways to study and utilise proteins are described.
  • The enzyme reaction mechanism has been elucidated at the atomic level.
  • Lysozyme is a model protein for studying on structure and function of proteins.
  • The diversities in structure and function make lysozymes interesting.
  • A new challenging reaction mechanism for hen lysozyme has been proposed.
  • Lysozyme has an antibacterial action.
  • Lysozyme has applications in medicines and food additives.
  • Some lysozymes are digestive enzymes.

Keywords: enzyme; catalysis; lysis; 3D structure; medicine; food additive; denaturation; stability

Figure 1. A substrate for lysozyme. Copolymer of N‐acetylmuramic acid (MurNAc) and N‐acetylglucosamine (GlcNAc) that is the constituent of bacterial cell walls. These sugar residues bind at sites C, D, E and F in Figure . The arrow shows the bond susceptible to lysozyme.
Figure 2. Three‐dimensional structure of hen lysozyme. Residues Glu35 and Asp52 are shown as the catalytic groups. Residues Trp62 and Trp63 are also shown. The letters A–F in the active‐site cleft schematically show the binding sites of each sugar residue of substrate, hexamer of N‐acetylglucosamine. The program MOLSCRIPT was used.
Figure 3. The reaction mechanism of lysozyme. The D‐sugar is distorted from the chair form to the half‐chair form upon binding. Glu35 donates a proton to the susceptible oxygen atom. A negative charge of Asp52 assists the formation of the oxocarbonium ion.


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Further Reading

Imoto T, Johnson LN, North ATC, Phillips DC and Rupley JA (1972) Vertebrate lysozymes. In: Boyer PD, Lardy H and Myrback K (eds) The Enzymes, 2nd edn, vol. 7, pp. 665–868. New York, NY: Academic Press.

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How to Cite close
Imoto, Taiji(Mar 2017) Lysozyme. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0000869.pub3]