Liver sialyltransferase activity

The subcellular distribution of rat liver sialyltransferase activity was first studied in fractions obtained by differential centrifugation (Schach-... 

Substrate-specificity studies on microsomal, frog-liver sialyltrans-ferase revealed the presence of (2—>3) and (2—>6) activities.277 This enzyme system readily sialylates oligosaccharides, but is almost inactive with asialofetuin, which is in contrast to the sialylation of oligosaccharides, as well as asialofetuin, by rat-liver sialyltransferase.278 The conclusion from this observation is that acceptor specificity of sialyl-transferases isolated from liver of evolutionary distant animals is similar for substrates of low molecular weight, but differs for compounds of high molecular weight.279... 

In the case of rat and human-breast cancer, an increase in serum-sialyltransferase activity is considered to be the consequence of both increased production and release, the latter perhaps through cell-surface shedding of the enzyme from the metastasizing, mammary-tumor cells.290 Accordingly, release of large amounts of sialyltransferase from hepatoma cell-lines derived from patients having hepatocellular carcinoma was observed, in contrast to cell lines derived from nomial human-liver.291 An increased level of sialyltransferase has been observed in regenerating rat-liver.292... 

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). 

Long term hormonal control functions in the expression of enzyme concentrations and de novo acceptor molecule synthesis in the case of sialyltransfer reactions. Examples in development have been cited (sections II.2, II. 3, and III. 10), and the regenerating liver has proved valuable in studies of this kind, e.g. UDP-GlcNAc 2-epimerase (Okubu et al. 1976, Okamoto and Akamatsu 1980). Elevation of enzyme concentration could be shown to be a function of de novo protein synthesis. Study of hormone effects (oestrogen, progesterone) on sialyltransferase activity and glycosidically linked sialic acid levels in the cervical cyclic phenomena have been reported (Moghissi and Syner 1976, Chantler and Debruyn 1977, Hatcher et al. 1977, Nasir-ud-Din et al. 1979, Wolf et al. 1980). Similar effects have been demonstrated in rat endometrium (Nelson et al. 1975). 

Fraser, I. H., Coolbear, T., Sarkar, M., and Mookerjea, S., 1984, Increase of sialyltransferase activity in the serum and liver of inflamed rats, Biochim. Biophys. Acta 799 102-105. 

McCaffrey, G., and J.C. Jamieson. 1993. Evidence for the role of a cathepsin D-like activity in the release of Gal beta 1-4 GlcNAc alpha 2-6 sialyltransferase for rat and mouse liver in whole-cell systems. Comp Biochem Phys C 104 91. 

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 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. ... 

The presence of glycosyltransferase activities at the surface of cells, i.e. located in the plasma membrane, remains controversial. Very low or no activity of sialyltransferases could be detected in rat kidney and liver plasma membrane... 

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