KDN-Sialidase is a novel sialidase that effectively cleaves a-ketoside of KDN (KDN=3-deoxy-D-glycero-D-galacto-non-2-ulopyranosonic acid) and also a-ketoside of Neu5Ac at a much slower rate. The ratio of 4-methylumbelliferyl-KDN- to 4-methylumbelliferyl-Neu5Ac-cleaving activity is about 30:1. One unit of enzyme cleaves 1 nmol of 4-methylumbelliferyl-KDN per minute at 37°C.