A sensitive assay of sialidase activity with fluorogenic oligosaccharide derivatives

Fluorogenic oligosaccharide derivatives, lactityl-aminopyridine and sialyllactityl-aminopyridines, were synthesized by reductive amination of lactose and sialyllactose with 2-aminopyridine in the presence of sodium cyanoborohydride. Lactityl-aminopyridine showed bluish-white fluorescence at 390 nm by excitation with ultraviolet light at 320 nm, and the intensity of the fluorescence was proportional to the concentration of lactityl-aminopyridine within a range from 20 to 9800 pmole/ml. Two isomers of sialyllactityl-aminopyridine were enzymatically hydrolyzed to sialic acid and lactityl-aminopyridine by the action of both microbial and mammalian sialidases, and their suitability as substrates for sialidase was investigated. The result showed that sialidase activity was determined with about 55-fold higher sensitivity than that of ordinarily used colorimetric methods.