Sclerotin
Sclerotin is a component of the
As it matures, freshly formed sclerotin becomes a hard, horn-like substance with a range of yellow-brown colors. As animals adapted to life on land, increasingly diverse needs for organic stiffening components arose (as opposed to mineral stiffening components such as calcium carbonates and phosphates). Among the invertebrates, this need was met largely by the development of sclerotins and other cross-linked proteins that allowed insects to adapt to existence on the land and later to develop wings.[3]
Sclerotin is biochemically variable; different species incorporate different proteins in different proportions, and the same insect will use different compositions in forming the different components of its body. For example, a caterpillar may have sclerotized jaws, head capsule, and legs, with the rest of the body soft and membranous. In general, sclerotized cuticle is formed by cross-linking the various protein molecules with phenolic compounds – a tanning process under enzymatic control.[1] In some of the Apterygota, however, at least some of the cross-linking is by disulphide bonds reminiscent of protein cross-linking in the formation of keratin.[4] This has led many authors to refer to such cross-linked proteins in invertebrates as keratin, but modern analyses have shown that the term is inappropriate; keratins are a fairly well-defined set of proteins comprising particular chains in different proportions cross-linked in particular ways. Invertebrate connective tissue proteins based on disulphide links appear to be radically different.[5][6]
See also
References
- ^ a b Chapman, R.F. (1969) The Insects: Structure and Function. Elsevier, New York. Chapter 22.37 - "Expansion of the new cuticle is brought to an end by the onset of tanning"
- ISBN 0486234703.
- ISBN 0412264609.
- ISBN 0-412-61390-5.
- ^ Weber, Klaus et al; "Amino acid sequences and homopolymer-forming ability of the intermediate filament proteins from an invertebrate epithelium"The EMBO Journal vol.7 no.10 pp.2995-3001, 1988
- doi:10.1038/166439a0