Purification of a low-molecular-weight, mucin-type glycoprotein from human submandibular-sublingual saliva.
A low-molecular-weight, monomeric, mucin-type glycoprotein (MG2) has been isolated from human submandibular-sublingual saliva. Initial purification involved sequential gel-filtration on Sephadex G-200 and Sepharose CL-2B, the latter in the presence of 6M urea. Fractions containing MG2 were next separated from contaminating secretory IgA by immunoaffinity chromatography or recycling through Sephadex G-200. Mucin fractions were 14C-labeled by reductive methylation, and then the final purification-step entailed recycling radiolabeled materials through Sephadex G-200. Radiolabeling aided in the assessment of purity, as judged by SDS-PAGE and ion-exchange chromatography. The carbohydrate portion accounted for 69.6% of the recovered weight and was composed of N-acetyl-glucosamine, N-acetylgalactosamine, galactose, fucose, and N-acetylneuraminic acid. Sulfate was also present. The protein comprised 30.4% of the recovered weight with threonine, serine, proline, and glycine accounting for 75.2% of the total amino acids. The oligosaccharides were alkali-labile, indicating an O-glycosyl linkage to the peptide. The mucin was weakly acidic and had an estimated mol. wt. of 200 000-250 000.
D000596:Amino Acids / Q000032:analysis; D002241:Carbohydrates / Q000032:analysis; D002850:Chromatography, Gel; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D046911:Macromolecular Substances; D008970:Molecular Weight; D009077:Mucins / Q000302:isolation & purification*; D012463:Saliva / Q000032:analysis*; D013361:Sublingual Gland / Q000378:metabolism; D013363:Submandibular Gland / Q000378:metabolism
D000596:Amino Acids; D002241:Carbohydrates; D046911:Macromolecular Substances; D009077:Mucins