Characterization of the Major Sialidases of Various Types of Rat Blood Cells: Their Comparison with Rat Liver Sialidases1

Abstract

The substrate specificity and subcellular location of the major sialidases of three types of rat blood cells were characterized and compared with those of the known three types of rat liver sialidase, which have been designated intralysosomal, cytosolic, and plasma membrane-associated sialidases. Platelets and leucocytes contain mainly an acid sialidase, which is highly active towards oligosaccharides and 4MU-NeuAc, and erythrocytes possess a high level of a sialidase acting on gangliosides. A Percoll gradient centrifugation study showed that the former is located in lysosomes and the latter in plasma membrane. When the sialidase was solubilized and partially purified from erythrocyte ghosts, the enzyme was found to hydrolyze actively gangliosides but only poorly other substrates such as 4MU-NeuAc, oligosaccharides, and glycoproteins. The sialidase partially purified from rat liver membrane fraction exhibited the same substrate specificity. It is concluded that the major sialidase of platelets and leucocytes corresponds to hepatic intralysosomal sialidase while erythrocytes contain almost exclusively a ganglioside sialidase which corresponds to hepatic plasma membrane sialidase.

Cloning and Characterization of NEU2, a Human Gene Homologous to Rodent Soluble Sialidases

“…Sialidases have been described in the lysosomal matrix as a single protein or associated with ␤-galactosidase and the carboxypeptidase protective protein/cathepsin A (PPCA) to form a large molecular mass complex (Verheijen et al, 1985) and as a polypeptide strictly associated with lysosomal membrane Miyagi and Tsuiki, 1984;Sagawa et al, 1990;Zeigler et al, 1989). In human a lysosomal sialidase is implicated in two lysosomal storage disorders: sialidosis, which is due to a structural alteration in the sialidase gene (Thomas and Beaudet, 1995), and galactosialidosis, in which the absence of PPCA is responsible for the combined lack of the two lysosomal hydrolases (d 'Azzo et al, 1995).…”

Sialidase in rabbit blood

“…Should the ability of erythrocyte sialidase to affect GDla and GM1 be linked to the chemical difference between the enzymes solubilized by detergent and phospholipase C, further study of the structure/function relationship of the sialidase activity towards gangliosides would be required. In addition, rat erythrocyte membrane sialidase showed little or no hydrolyzing activity towards MeUmb-NeuAc, sialyllactose, fetuin and orosomucoid [13]. However, rabbit erythrocyte membrane sialidase exhibited high activity towards MeUmb-NeuAc, sialyllactose and glycopeptides but no activity towards the glycoproteins tested.…”

“…It has been reported that no sialidase activity toward MeUmb-NeuAc or mixed gangliosides was found in cytosolic fractions of erythrocytes, platelets and leucocytes from rat blood cells [13]. Human leucocyte sialidase activity was also not detected in the cytosolic fraction [34].…”

“…; never been studied but it might be caused by activalion of the platelets because platelets contain several granulies and degradation occurs by the activation of platelets. In order to characterize platelet sialidase, rat platelets were prepared from heparinized blood [13], but human platelets were prepared in acid/citrate/glucose [35] while the present rabbit platelets were prepared in sodium citrate. It is known that some preparations of commercially available heparin induce spontaneous platelet aggregation [38] so it is possible that rat platelet sialidase was not present in the cytosolic fraction because of activation of the platelets.…”

“…Previously, the partial purification and characterization of sialidase from human [12] and rat [13] erythrocyte membranes have been reported; however, erythrocyte membrane sialidase has not been highly purified. In this work, sialidase activities in rabbit blood cells and serum were measured and the ganglioside-hydrolyzing sialidase was highly purified from erythrocyte membranes as a major sialidase in the blood.…”