Cell wall chemistry: Which enzyme specifically hydrolyzes the murein (peptidoglycan) of bacterial cell walls?

Introduction / Context:
Peptidoglycan (murein) is the structural polymer that provides bacterial cells with rigidity and resistance to osmotic lysis. Certain host defenses and laboratory reagents target this polymer. Identifying the enzyme that hydrolyzes key bonds in murein is fundamental for understanding innate immunity and bacteriolysis.

Given Data / Assumptions:

• Murein is composed of repeating N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) units.
• We are focusing on enzymatic hydrolysis of the glycan backbone.
• Common enzymes under consideration include lysozyme and non-related hydrolases.

Concept / Approach:

Lysozyme cleaves the beta-1,4 glycosidic bond between NAG and NAM residues in peptidoglycan. It is abundant in human secretions (tears, saliva), egg white, and phagolysosomes. Cleavage compromises cell wall integrity, particularly in Gram-positive bacteria where peptidoglycan is more exposed.

Step-by-Step Solution:

Verification / Alternative check:

Laboratory assays show rapid clearing of bacterial suspensions upon lysozyme addition. Electron microscopy confirms wall degradation. Resistance varies with Gram status and outer membrane protection in Gram-negatives.

Why Other Options Are Wrong:

• Peroxidase: involved in oxidative reactions, not peptidoglycan hydrolysis.
• Tannase: hydrolyzes tannins, irrelevant to bacterial cell walls.
• None of these: incorrect because lysozyme is correct.

Common Pitfalls:

• Assuming lysozyme targets peptide cross-bridges; it targets the glycan backbone, not peptide stems.
• Overlooking outer membrane shielding in Gram-negatives that limits lysozyme access unless permeabilized.

Final Answer:

Lysozyme