Sclerotin

Definition

A hardened, insoluble protein complex formed in the arthropod cuticle by sclerotization, in which quinones enzymatically cross-link adjacent protein chains. Sclerotin imparts rigidity and durability to chitinous exoskeletons without the brittleness of pure mineralization, allowing flexibility in joints while providing armor in sclerites, mandibles, and chelicerae. The degree of sclerotization varies regionally across the body and ontogenetically through molting cycles.

Etymology

From Greek skleros (hard) + -in (chemical suffix)

Example

The dark, rigid mandibles of a carabid beetle consist largely of heavily sclerotized cuticle, contrasting with the pale, flexible membranes of the cervical region where sclerotization is minimal.

Synonyms

• sclerotized protein
• tanned cuticle protein

Related Terms

• Sclerotization
• Cuticle
• Exoskeleton
• Chitin
• Sclerite
• melanization
• tanning (biochemistry)
• Ecdysis

Usage Notes

Distinguished from chitin, the polysaccharide scaffold of the cuticle, and from calcification or mineralization seen in crustaceans. Sclerotin is the proteinaceous component that has undergone quinone tanning; the process (sclerotization) and product (sclerotin) are often conflated in casual usage. Dark coloration often correlates with degree of sclerotization due to quinone-derived pigments, though melanin may also contribute.