title: Structure and function of mucus.
abstract: A glycoprotein building block is common to mammalian mucins. This structure is composed of several protein chains having the same sequence. The carbohydrate side chains, which constitute over three-quarters of the weight, coat only some two-thirds of the backbone chain. The bare protein chains are linked by disulphide bridges and can be digested away with trypsin. Either procedure rapidly solubilizes mucus and results in a structural unit of about 500 000 molecular weight. Mucus solubilizes spontaneously. The first size unit which reaches solution is about 15 X 10(6) molecular weight but continues to break down further. Mechanical agitation considerably speeds up this process. The gel-like character which is an essential feature of mucus--which cannot otherwise act as transport coupler--is thus a transient phenomenon. The problem of how such a structure can arise from the building blocks known to be available is discussed.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport; D002417:Cattle; D004848:Epithelium / Q000378:metabolism; D006801:Humans; D008968:Molecular Conformation; D008970:Molecular Weight; D009077:Mucins / Q000032:analysis*; D009093:Mucus / Q000378:metabolism / Q000648:ultrastructure*; D011487:Protein Conformation; D014783:Viscosity
chemical_list: D009077:Mucins