Studies on the occurrence of disialosyl groups in glycoproteins of salivary glands.

The major glycoprotein of pig submandibular and rat sublingual glands were investigated for the presence of disialosyl groups. The content of (C-8)-substituted sialic acid in the glycoproteins was determined by three different procedures: colorimetric, periodate oxidation and permethylation. Approximately 13% of sialic acid in pig submandibular glycoprotein, but none in rat sublingual glycoprotein, contained a substituent at C-8. This substituent was identified as sialic acid from its susceptibility to neuraminidase treatment. From our estimation, it appears that one out of four sialic acid residues in pig submandibular glycoprotein occurs in an N-acylneuraminyl-alpha(2 leads to 8)-N-acylneuraminyl group.