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The rate of release of amino acids during partial acid hydrolysis of bovine submaxillary mucin has been studied. A number of di- and tripeptides have been isolated on the amino acid analyzer. Three β-hydroxyamino acid peptides, Thr-Thr-Thr, Ser-Ser, and Thr-Ser have been isolated and account for 12 % of these amino acids in native mucin. A substantial amount of the glycine and alanine has been isolated as dipeptides of serine and threonine with the fihydroxyamino acids in the amino-terminal position. Proline, valine, isoleucine, and leucine seem to be in close association in the peptide core. The same pattern of peptides has been obtained from the partial acid hydrolysis of ovine submaxillary mucin.

A secretory glycoprotein was isolated from the hamster sublingual gland. It contains 65% carbohydrates, the remainder being protein. The principal type of sialic acid was identified as N-acetylneuraminic acid with about 1/4 of the molecules O-acetylated. The hexosamine occurs mainly as N-acetylgalactosamine; other sugars present are galactose and fucose. The carbohydrate side chains are linked to the protein core by an O-glycosyl linkage between seryl and threonyl residues and N-acetylgalactosamine. The glycoprotein has an apparent molecular weight of 330,000. The sialogly coprotein may act as a biological antifreeze. Relevant differences in the chemical composition of the secretory glycoproteins of the sublingual and submaxillary salivary glands of this species are briefly discussed.