Enzymatic synthesis of the protein-hexosamine linkage in sheep submaxillary mucin.

A particulate enzyme preparation, obtained from sheep submaxillary gland, catalyzed the transfer of iV-acetyl-Dgalactosamine from its uridine diphosphate derivative to certain protein acceptors. The proteins were prepared from sheep submaxillary mucin by enzymatic or chemical treatments that removed the disaccharide residues from the mucin. Only these proteins served as N-acetylgalactosamine acceptors. The N-acetylgalactosamine glycosidic bonds in the product were alkali-labile, suggesting that they were linked to the hydroxyamino acid residues. The high degree of specificity exhibited by the transferase indicates that it catalyzes the first step in the conversion of the protein to this type of glycoprotein.