title: Chitin helicoids accompany protein helicoids in the periostracum of a whelk, Buccinum.
abstract: The periostracum of the marine gastropod Buccinum has a helicoidal arrangement of its principal constituent which is a fibrous protein (Hunt and Oates, 1978). Chitin, chemically and physically identified, is present at a concentration of about 6% of the dry weight and can be seen in dispersates of whole periostracum as long fibrils and ribbons between 3 and 14 nm diameter. Deproteinization with hot alkali removes all protein leaving a chitinous 'ghost' of the periostracum. Dispersates, examined negatively stained, show only chitin fibrils and ribbons while sectioned material demonstrates a tenuous, part orthogonal, part helicoidal, architecture based on the chitin residue. The relative roles of the protein and polysaccharide components is speculated upon and comparisons with arthropod cuticle drawn.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002686:Chitin / Q000378:metabolism*; D008854:Microscopy, Electron; D008974:Mollusca / Q000033:anatomy & histology* / Q000378:metabolism; D011506:Proteins / Q000378:metabolism
chemical_list: D000596:Amino Acids; D011506:Proteins; D002686:Chitin