ABSTRACT
Chitin is the most abundant organic compound of nitrogen. At least 10 gigatons (1.10
kg) of chitin are synthesized and degraded each year in the biosphere. Chitin
is therefore important for making nitrogen available to countless living organisms: it is widely distributed among invertebrates. Nitrogen fixation from the atmosphere is made by
Rhizobium
in root nodules of leguminous plants, the major step being the formation of lipo-chitin oligomeric forms. Alpha-chitin is found in the calyces of hydrozoa, the egg shells of nematodes and rotifers, the radulae of mollusks, and the cuticles of arthropods, and beta-chitin is in the shells of brachiopods and mollusks, the cuttlefish bone, the squid pen, and pogonophora tubes. Chitin is found in exoskeletons, peritrophic membranes, and cocoons of insects. The septation apparatus in budding yeast is based on a chitin septum. Chitin is ubiquitous in the fungi: the chitin in the fungal walls varies in crystallinity, degree of covalent bonding to other wall components, mainly glucans, and degree of acetylation.
