Sclerotization is a biochemical process that produces the rigid shell of

sclerotin Sclerotin is a component of the cuticle of various Arthropoda, most familiarly insects. It is formed by cross-linking members of particular classes of protein molecules, a biochemical process called sclerotization, a form of tanning in which qu ...

that comprises an insect's chitinous exoskeleton. It is prominent in the thicker, armored parts of

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three ...

s and

arachnid Arachnida () is a class of joint-legged invertebrate animals (arthropods), in the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, harvestmen, camel spiders, whip spiders and vinegar ...

s, especially in the biting mouthparts and

sclerite A sclerite (Greek , ', meaning " hard") is a hardened body part. In various branches of biology the term is applied to various structures, but not as a rule to vertebrate anatomical features such as bones and teeth. Instead it refers most commonly ...

s of scorpions and beetles.

Molecular mechanism

Sclerotization entails crosslinking of oxygen-reactive derivatives of dopamine. The reaction of the dopamine derivatives toward oxygen is catalyzed by diverse enzymes such as laccase, which convert the

catechol Catechol ( or ), also known as pyrocatechol or 1,2-dihydroxybenzene, is a toxic organic compound with the molecular formula . It is the ''ortho'' isomer of the three isomeric benzenediols. This colorless compound occurs naturally in trace amoun ...

groups to quinones. The resulting quinones are susceptible to

nucleophilic attack In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are ...

by amines and thiols, which decorate the side-chains of proteins. These reactions gives rise to color (typically brown), loss of solubility, and rigidification that accompany sclerotization.{{cite journal , doi=10.1007/s00726-005-0298-2, title=When Quinones Meet Amino Acids: Chemical, Physical and Biological Consequences, year=2006, last1=Bittner, first1=S., journal=Amino Acids, volume=30, issue=3, pages=205–224, pmid=16601927, s2cid=22027672 SclerotizationReaction

References

Structural proteins

Molecular mechanism

See also

References