Studies of mucin-type glycoproteins: Olefinic amino acids, products of the β-elimination reaction

Abstract

The carbohydrate moieties of mucin-type glycoproteins are attached to the polypeptide core by O-glycosyl linkages of N-acetylgalactosamine to the hydroxyl groups of both serine and threonine. Alkali catalyzes the release of the carbohydrate groups by a β-elimination reaction. Studies reported here on the relative rates of the β-elimination reaction have demonstrated that serine-linked glycosides are released more rapidly than threonine-linked glycosides. The ratio of glycosylated serine to glycosylated threonine can readily be determined after β-elimination. The olefinic amino acids, which are products of the β-elimination reaction, are converted into pyruvate and α-ketobutyrate by acid hydrolysis and then are assayed spectrophotometrically with lactate dehydrogenase. In addition, the olefinic amino acids formed upon alkali treatment of pig submaxillary mucin have been further identified by preparation of the dinitrophenylhydrazone derivatives of the α-keto acids and their conversion to α-amino acids by catalytic hydrogenolysis.