DISTRIBUTION IN SPLEEN SUBCELLULAR ORGANELLES OF SIALIDASE ACTIVE TOWARDS NATURAL SIALOGLYCOLIPID AND SIALOGLYCOPROTEIN SUBSTRATES

A procedure was devised for the preparation of enriched populations of subcellular organelles from homogenized bovine spleen. The fractions obtained were characterized for arysulfatase, succinate dehydrogenase, UDPgalactosyltransferase and 5′-nucleotidase activities. The distribution of sialidase (acylneuraminyl hydrolase, EC 3.2.1.18) activity directed towards either endogenous substrate or exogenous ganglioside substrate suggests that it is enriched in the plasma membrane/microsomal fractions. Sialidase activity towards exogenous sialoglycoproteins, isolated from erythrocyte membranes, was enriched in the least dense of the plasma membrane/microsomal-containing fractions. The endogenous sialidase substrates were primarily the sialoglycolipids, hematoside and disialogangliosides. At the pH optimum, 3.8 and 37°C, release of endogeneous sialic acid was linear with time for 3 h. At the end of this time, 85% or more of the available endogenous substrate was hydrolyzed. © 1979.