The murine sublingual and submandibular mucins. Their isolation and characterization.

From the mouse sublingual and submandibular glands high-molecular weight glycoproteins (mucins) were isolated. These mucins appeared to be homogeneous in polyacrylamide gel electrophoresis and in the analytical ultracentrifuge. S20,W values of 10.9 and 5.5 were found for the sublingual and submandibular mucin respectively. With sodium dodecyl sulfate or N-acetylcysteine no subunits could be detected. Both mucins consisted for about 1/3 of protein and 2/3 carbohydrate. Their mucin character was also denoted by the high content of serine plus threonine. Respectively 42 mol% and 34 mol% of the protein core of the sublingual and submandibular mucins consisted of these amino acids. The main sugars in these mucins were sialic acid, galactosamine, galactose, glucosamine and mannose. The molar ratio for the sublingual and submandibular mucin being 1.00 : 1.03 : 1.08 : 0.26 : 0.23 and 1.00 : 0.71 : 1.10 : 0.65 : 0.53, respectively. The sialic acid content of both mucins was about 25%. Fucose and sulfate, on the other hand, were less than 1%. The presence of sulfate was also indicated by preliminary studies in vivo on the incorporation of [35SO4] sulfate.