Partial characterization and studies of fibroblast and leucocyte neuraminidase activities towards sialyloligosaccharides in adult sialidosis and mucolipidosis II and III

We described the partial characterization and some properties of fibroblast and leucocyte neuraminidase towards 2 → 3 and 2 → 6 sialyllactose, and 2 → 3 and 2 → 6 sialylhexasaccharide which were isolated from the urine of a patient with adult sialidosis with partial β-galactosidase deficiency. Neuraminidase activities were assayed using the radioactive-labeled derivatives of these saccharide substrates. These neuraminidases (acylneuraminyl hydrolase, EC 3.2.1.18) were partially inactivated by homogenization, sonication and freeze-thawing treatment. The leucocyte neuraminidase was more labile than that of fibroblasts. Fibroblast neuraminidase had about a 10-fold higher activity than leucocyte neuraminidase towards the respective substrates. The neuraminidase from fibroblasts and leucocytes were each able to hydrolyze 2 → 3 isomers 2–3-times faster than 2 → 6 isomers and the sialyllactoses 1.5–3.0-times faster than sialylhexasaccharides. Neuraminidase activities towards all four substrates were deficient in fibroblasts and leucocytes from the patients with adult sialidosis. Loss of activity was especially prominent in fibroblasts, while considerable residual activities (about 20–30%) remained in leucocytes. In mucolipidosis II and III patients, these neuraminidase activities showed normal levels in leucocytes, although they were decreased in fibroblasts. The discrepancy between neuraminidase activities towards 2 → 3 and 2 → 6 isomers was not found in all the cases.