Neuraminidase-sialyltransferase

AMP deaminase neuraminidase leucy1-3-naphthylamidase p-nitrophenyIphosphatase inorganic pyrophosphatase nucleotide pyrophosphatase sialyltransferase NADH oxidase... 

The chemical relationship of the seven forms of human liver a-L-fucosidase has been studied by isoelectric focusing of neuraminidase and sialyltransferase-treated preparations of a-L-fucosidase. Neuraminidase treatment leads to a decrease in the activity of the more-acidic forms, and a concomitant increase in the activity of the more-neutral forms. Incubation of the neuraminidase-treated enzyme forms with a radiolabelled CMP-neuraminic acid and sialyl-transferase led to generation of more-acidic forms of the enzyme. The seven isoenzymes were separated by preparative isoelectric focusing and were characterized kinetically and immunochemically. 

The requirements for the rat and pork liver sialyltransferases are shown in Table VI. The need for exogenous acceptor is almost absolute and neuraminidase-treated i-acid glycoprotein is far more eflFective than other derivatives, indicating that a terminal galactose residue is required for acceptor activity. The sialyltransferases show no requirements for cations, and the pH optima are 5.7 and 7.0 for the rat and pork liver enzymes, respectively. The Km values for the pork liver enzyme are 0.19 mM for the nucleotide sugar and 0.9 mM for the glycoprotein acceptor (calculated on the basis of available acceptor sites). 

The receptor specificity of Sendai vims was first analyzed in studies employing gangliosides [136, 137] and erythrocytes that contained defined sialyloligosac-charides after neuraminidase and subsequent sialyltransferase treatment [138]. These studies showed that Sendai vims has a preference for a2-3-bound... 

The incorporation of A-acetylneuraminic acid from the CMP-nucleotide derivative into neuraminidase-treated human lipoproteins of very low density was catalysed by preparations from porcine liver microsomes. The activity of the CMP-A -acetylneuraminic acidiglycoprotein sialyltransferase present in rat-liver microsomes has been shown to be stimulated by UDP, but to be inhibited by CMP. The functions of glycosyltransferases in the processes of recognition and binding of asialoglycoproteins in liver have been investigated. ... 

On the basis of a concentration of 2.4 x 10 molecules of sialic acid per cell, a high sialyltransferase activity, and a measurable neuraminidase activity at the surface of the human blood platelet, Bosmann (1972) proposed that platelet aggregation could result from an interaction, at the surface of the cell, between the sialyltransferases and the galactosyl residues liberated by the action of the neuraminidase. This application of Roseman s (1970) theory to platelet aggregation would require a dynamic equilibrium of transfers and removals of sialic acid residues, with continuous formation, degradation, and reformation of the enzyme-substrate complexes. 

Following treatment of the fucose-labeled glycopeptides derived from the surfaces of RSV-BHK cells with neuraminidase, the radioactive products appeared similar to glycopeptides from normal cells (Warren et al., 19726). These results suggested that increased sialic acid content may account for the higher molecular weight of the glycopeptides from transformed cells. When sialyltransferase activity was as-... 

Sialyltransferase activities in normal and virally transformed mouse 3T3 cells have also been measured with specific endogenous acceptors (Bosmann, 1972a). The acceptors were prepared by incubating the intact cells with neuraminidase and then trypsin. The desialylated material released from the cells was used to measure sialyltransferase activity in crude detergent extracts of the cells. Cells transformed by MSV, RSV, or Py had more acceptor and transferase activity than normal 3T3 cells. Surface sialyltransferase activity as measured by the ability of intact cells to transfer sialic acid- C from CMP-NANA- C to undefined surface acceptors was also higher in the transformed lines (Bosmann, 1972 ). 

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