Which of the following enzymes is primarily responsible for cross-linking collagen molecules during the maturation phase of wound healing?

Explanation

## Collagen Cross-Linking in Wound Maturation **Key Point:** Lysyl oxidase is the critical enzyme that catalyzes the oxidative deamination of specific lysine and hydroxylysine residues in collagen and elastin, converting them to aldehydes (allysine and hydroxyallysine). These aldehydes then spontaneously condense to form covalent cross-links between collagen molecules. **High-Yield:** This cross-linking process: - Occurs during the **maturation/remodeling phase** (weeks 3–12 and beyond) - Increases tensile strength of the wound progressively - Requires **vitamin C as a cofactor** (hydroxylation of lysine residues) - Is inhibited by **lathyrogens** (e.g., β-aminopropionitrile), which block lysyl oxidase **Clinical Pearl:** Deficiency of vitamin C (scurvy) or copper (a cofactor for lysyl oxidase) impairs collagen cross-linking, resulting in poor wound strength and dehiscence. ## Comparison of Related Enzymes | Enzyme | Function | Phase | Effect on Wound | | --- | --- | --- | --- | | **Lysyl oxidase** | Cross-links collagen via aldol condensation | Maturation | ↑ Tensile strength | | **Collagenase** | Degrades collagen (MMP-1) | Remodeling | Breaks down excess collagen | | **MMP-2** | Degrades collagen and gelatin | Inflammatory/remodeling | Tissue remodeling | | **TIMP** | Inhibits MMPs | All phases | Prevents excessive degradation | **Mnemonic:** **LOX = Lysyl Oxidase = Cross-linking** — remember that LOX is the enzyme that "locks" collagen molecules together.