Localization of sialidase in the plasma membrane of rat liver cells.

Sialidase activity towards ganglioside substrate, including hematoside, paralleled activity of 5’-nucleotidase and was found to be enriched in the plasma membrane fractions (TOUSTER, O., ARONSON, N. N., Jr., DULANEY, J. T., AND HENDRICKSON, M. (1970) J. CelZ. Biol. 47, 604) prepared from rat liver cells. Lesser sialidase activity towards ganglioside substrate was found in fractions (LEIGHTON, F., POOLE, B., BEAUFAY, H., BAUDHUIN, P., COFFEY, J. W., FOWLER, S., AND DEDUVE, C. (1968) J. Cell. Biol. 37, 482) containing the lysosomal marker, acid phosphatase. Concentration of gangliosides, and total bound sialic acid per mg of protein, also paralleled the plasma membrane marker, 5’nucleotidase. Subcellular fractions were prepared from rat liver cells by a recently developed procedure (Touster et ~2.) which favors the isolation of the plasma membrane fraction, and by an independent method (Leighton et al.) favoring the isolation of lysosomes. These findings indicate that a major fraction of sialidase with activity towards ganglioside substrate is localized in the plasma membrane of the liver cell, and that ganglioside substrate is also localized in this cellular structure.