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Sclerotization is a biochemical process that produces the rigid shell of sclerotin that comprises an insect's
chitin
Chitin ( C8 H13 O5 N)n ( ) is a long-chain polymer of ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is probably the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chit ...
ous 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 pairs ...
s and arachnids, especially in the biting mouthparts and sclerites of scorpions and beetles.
Molecular mechanism
Sclerotization entailscrosslinking Cross-linking may refer to
*Cross-link
In chemistry and biology a cross-link is a bond or a short sequence of bonds that links one polymer chain to another. These links may take the form of covalent bonds or ionic bonds and the polymers ca ...
of oxygen-reactive derivatives of dopamine
Dopamine (DA, a contraction of 3,4-dihydroxyphenethylamine) is a neuromodulatory molecule that plays several important roles in cells. It is an organic compound, organic chemical of the catecholamine and phenethylamine families. Dopamine const ...
. The reaction of the dopamine derivatives toward oxygen is catalyzed by diverse enzymes such as laccase
Laccases () are multicopper oxidases found in plants, fungi, and bacteria. Laccases oxidize a variety of phenolic substrates, performing one-electron oxidations, leading to crosslinking. For example, laccases play a role in the formation of lign ...
, which convert the catechol groups to quinone
The quinones are a class of organic compounds that are formally "derived from aromatic compounds
s. The resulting quinones are susceptible to uch as benzene or naphthalene
Uch ( pa, ;
ur, ), frequently referred to as Uch Sharīf ( pa, ;
ur, ; ''"Noble Uch"''), is a historic city in the southern part of Pakistan's Punjab province. Uch may have been founded as Alexandria on the Indus, a town founded by Alexand ...
by conversion of an even number of –CH= groups into –C(=O)– groups with any necessary rearrangement of double ...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
See also
* Sclerotin * ScleriteReferences