A mucus glycoprotein of the duodenal gland is characterized. The glycoprotein was isolated from a water-soluble homogenate fraction of the submucosal tissue of the most proximal part of the small intestine, containing the duodenal gland, and was purified from contaminating protein by two sequential equilibrium-centrifugation steps in CsCl density gradients. Structural analysis of the purified glycoprotein showed two regions in the protein core: one part characterized by the presence of essentially all of the cysteine residues and another by the presence of most of the serine and threonine. Carbohydrate was found linked to the latter part. Rat [1.] and human duodenal gland mucus glycoprotein show homology in chemical composition. Both glycoproteins have a relatively high protein content and contain little sulfate and no neuraminic acid. In man the mucus glycoprotein, however, has a higher content of serine plus threonine, a lower content of N-acetylglucosamine, a slightly higher content of fucose, and a lower molar ratio of N-acetylgalactosamine relative to serine plus threonine
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