Double labeling on the two faces of the same section with lectin-gold and silver enhancement. Ultrastructural detection of the terminal disaccharides sialic acid-beta-galactose and sialic acid-alpha-N-acetylgalactosamine

The double-labeling with protein A-gold performed on the two faces of the tissue sections requires protein A-gold complexes with different gold particle size. To avoid artifacts and steric hindrance phenomena related to the gold size, an approach was developed making use of protein A-gold complex of 10 nm on both faces and silver enhancement of gold signal on one side only. Present data also confirmed that among the polymorphous secretory granules of the mouse parotid gland, only the darker regions of the target granules secrete sialoglycoconjugates containing sialic acid linked to beta-galactose while the paler regions of bizonal granules secrete sialoglycoconjugates characterized by terminal sialic acid linked to alpha-D-N-acetylgalactosamine and containing C4 acetylated residue