An activator protein of oligosaccharide sialidase

beta-Glucosidase-stimulating proteins have been purified from human brain. One of these proteins also activated oligosaccharide sialidase activity in fibroblasts from galactosialidosis and sialidosis patients and in control cells but was not able to stimulate residual sialidase from I-cell disease fibroblasts. Activation was observed with either sialyl-oligosaccharides and -glycoproteins or the artificial substrate MU-NANA. The activator did not stimulate ganglioside sialidase from control and mucolipidosis IV fibroblasts. Column chromatography, polyacrylamide electrophoresis or desialylation treatment of the activator did not achieve separation of the stimulating abilities toward beta-glucosidase and sialidase.