DIFFERENTIAL REACTIVITY OF 2 TYPES OF N-GLYCOLYLNEURAMINIC ACID DIMERS TOWARD ENZYMATIC AND NONENZYMATIC HYDROLYSIS OF THEIR INTERKETOSIDICLINKAGES

The kinetics of acid- and sialidase-catalyzed hydrolysis of the interk etosidic linkages of two different disialic acids, Neu5Gc alpha 2-->5- O(glycolyl)Neu5Gc and Neu5Gc alpha 2-->8Neu5Gc, were studied. The form er sequence was recently identified in the polysialic acid chains of a sialic acid-rich glycoprotein isolated from the egg jelly coat of two different species of sea urchins, and the latter was previously found in the cortical alveolar-derived polysialoglycoprotein from rainbow t rout eggs. At pH values < 3.8, the rate of hydrolysis of Neu5Gc alpha 2-->5-O(glycolyl)Neu5Gc was greater than that of Neu5Gc alpha 2-->8Neu 5Gc. Paradoxically, however, Neu5Gc alpha 2-->5-O(glycolyl)Neu5Gc was more stable than Neu5Gc alpha 2-->8Neu5Gc at pH values > 3.8. These fi ndings indicate a greater contribution of intramolecular general acid catalysis to the lability of the alpha 2-->5-ketosidic linkage. Neu5Gc alpha 2-->5-O(glycolyl)Neu5Gc was a poor substrate for Arthrobacter u reafaciens, Clostridium perfringens, and Vibrio cholerae sialidases, i n contrast to Neu5Gc alpha 2-->8Neu5Gc. Neu5Gc alpha 2-->5-O(glcolyl)N eu5Gc was essentially resistant to hydrolysis by A. ureafaciens sialid ase. (C) 1994 Academic Press, Inc.