A Novel Sialidase Capable of Cleaving 3-Deoxy-D-glycero-D-galacto-2-nonulosonic Acid (KDN)

We have examined the tissues of several species of fish and found that the liver of the loach (Misgurnus fossilis) contains a novel sialidase capable of efficiently hydrolyzing 3-deoxy-D-glycero-D-galacto-2-nonulosonic acid (KDN) from the 4-methylumbelliferyl α-ketoside of KDN, KDNα2 → 3Galβ1 → 4GlcCer and KDNα2 → 6N-acetylgalactosaminitol as well as Neu5Ac from the 4-methylumbelliferyl α-ketoside of Neu5Ac and GM3. The pH optimum for this enzyme was determined to be 4.6, and the Km using the 4-methylumbelliferyl α-ketoside of KDN and 4-methylumbelliferyl α-ketoside of Neu5Ac as substrates were 0.07 and 0.12 mm, respectively. The enzyme was stable in the pH range of 4 to 5 but very unstable above pH 6. This is the first report of a sialidase capable of efficiently cleaving glycosidically linked KDN.