Biological context
First enzyme to have its 3D structure solved (Phillips, 1965). Present in tears, saliva, egg white — part of innate immunity against Gram-positive bacteria.
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Hydrolase / glycosidase · Glycoside hydrolase family 22
Hen egg-white lysozyme
EC EC 3.2.1.17PDB 1AKIGallus gallus
The archetype of mechanistic enzymology. Cleaves β-1,4 glycosidic bonds in bacterial peptidoglycan through an oxocarbenium-ion intermediate.
Mechanistic insight
Koshland refined the mechanism in 1953 using lysozyme — the classic retaining glycosidase textbook case. Glu35 acts as the general acid and Asp52 stabilises the covalent glycosyl-enzyme intermediate.
glycoside hydrolaseoxocarbeniumretainingmonomericclassic
Catalytic mechanism
Type: Double-displacement retaining glycosidase (covalent intermediate)
Rate-limiting: Hydrolysis of the covalent glycosyl-enzyme intermediate
Overall reaction
Peptidoglycan-(NAG-β1,4-NAM)n + H2O → Peptidoglycan fragments
01
Substrate binding and distortion
The peptidoglycan hexasaccharide binds along the A–F subsite cleft. The sugar in subsite D is forced into a strained half-chair / 1,4-boat conformation, pre-organising it for reaction by destabilising the ground state (Koshland's 'substrate distortion').
A:35A:52A:62A:63
Trp62, Trp63 and Trp108 line the substrate cleft and provide stacking contacts with the sugar rings.
Step 1 / 5
References (3)
- Vocadlo DJ, Davies GJ, Laine R, Withers SG. Catalysis by hen egg-white lysozyme proceeds via a covalent intermediate. Nature 412:835–838 (2001).
- Phillips DC. The hen egg-white lysozyme molecule. Proc Natl Acad Sci USA 57:483–495 (1967).
- Koshland DE. Stereochemistry and the mechanism of enzymatic reactions. Biol Rev 28:416–436 (1953).
Kinetic parameters
Steady-state kcat, KM and specificity constants from literature.
| Substrate | kcat (s⁻¹) | KM (mM) | kcat/KM (M⁻¹s⁻¹) | pH | T (°C) | Source |
|---|---|---|---|---|---|---|
| Micrococcus lysodeikticus cell walls | 0.500 | 0.0060 | — | 5.3 | 25 | BRENDA (aggregate literature) |
| (GlcNAc)6 chitohexaose | 0.500 | 0.080 | 6.25 × 10³ | 5 | 25 | Maksimainen et al., J. Mol. Biol. 2013 |
| p-Nitrophenyl-(GlcNAc)2 | 0.0220 | 0.65 | — | 5 | 40 | SABIO-RK |
Lysozyme turnover is slow for a hydrolase. Hydrolysis of the covalent glycosyl-enzyme intermediate is the rate-limiting step at neutral pH. Activity peaks near pH 5.
Michaelis–Menten · steady-state simulator
Run Lysozyme in silico.
Integrate the reaction v = Vmax·[S] / (Km,app + [S]) in closed form with RK4, across any [S], [E], and an optional reversible inhibitor. Defaults are drawn from the curated kinetic record for this enzyme where available.
Progress curve · [S](t) and [P](t)30 s window
substrate [S]product [P]
Saturation · v vs. [S]Km,app = 6.00e-3 mM · Vmax,app = 5.00e-4 mM/s
Inhibitor
Curated kinetic record
Defaults seeded from Micrococcus lysodeikticus cell walls at pH 5.3 / 25 °C — source: BRENDA (aggregate literature).
Why this enzyme is in the catalog
Ideal for teaching: small, monomeric, well-understood mechanism, abundant kinetic data, thousands of PDB entries for mutants.