Lectin histochemistry of secretory and cell-surface glycoconjugates in the ovine submandibular gland

Abstract

Information about the chemical structure of ovine submandibular glycoconjugates was obtained in situ by means of a battery of peroxidase-conjugated lectins with affinity for specific terminal or internal sugars or sugar sequences in conjunction with neuraminidase digestion and periodate oxidation. Stored secretions in all mucous acinar cells contained disaccharide side chains consisting of N-acetylneuraminic acid linked to penultimate alpha-N-acetylgalactosamine localizing the predominant disaccharide demonstrated biochemically. A previously unrecognized disaccharide consisting of terminal N-acetylneuraminic acid and penultimate beta-galactose was found in 20-30% of mucous acinar cells. Occasional clusters of acini composed purely of serous cells contained an additional unrecognized glyco-conjugate with oligosaccharides terminated by sialic acid with O-acetylated polyhydroxyl side chains and penultimate beta-galactose. Serous demilunes, however, lacked detectable complex carbohydrate other than glycogen. Terminal sialic acid-beta-galactose dimers were present on the apical surface of all ducts except for intercalated ducts coated only with neutral glycoconjugate. Fucose assayed biochemically as a minor component occurred in abundance in glycoconjugates at the apical surface of all intercalated and most striated duct cells and within some striated duct cells. Terminal alpha-galactose not previously detected biochemically was localized at the apex of all duct cells. These results provide new knowledge concerning the structure of ovine submandibular glycoconjugates. They also illustrate the value of histochemical methods for elucidating the diversity of complex carbohydrates in an organ, locating different glycoconjugates in different types or subtypes of epithelial cells and demonstrating intracellular sites that contain complex carbohydrate.