Fetuin glycoprotein study

Glycoprotein Galactosyltransferase Assays. In order to further investigate the effects of TPA and RA on glycoconjugate metabolism, UDP-galactose DSG-fetuin galactosyltransferase activity was assayed. Table II shows the results of this study. The effects of TPA and RA on... 

The Km value for exogenously added GM is 0.2 mM, which is identical to the value obtained with the chick embryonic brain (24) but is lower than the value reported for the rabbit neurohypophysis (25). Substrate inhibition at high glycolipid concentration as observed with other glycosyltransferases (22,26,27) was also noted in this study when the concentration of GM was above the Km (15). The Km value of the exogenously added DS-fetuin is 0.15 mM or 1.2 mM in terms of acceptor sites (15). This value is only one third of that obtained for desialylated a -acid glycoprotein which is a much less efficient acceptor than DS-fetuin (23). 

The strategy used to perform the PMP oligosaccharide profile analysis, with the use of bovine fetuin as a model system, is given in Scheme 1. Bovine fetuin, a major glycoprotein in fetal calf serum, has been widely used as a model for the study of glycoprotein structure. This glycoprotein contains both N- and O-linked oligosaccharides and detailed structural information is available (9-11). 

Table V shows that pork liver sialyltransferase will catalyze the transfer of sialic acid to galactosyl-( 8, l->4)-lV-acetylglucosaminyl-R, where R may represent a hydrogen atom or a complex macromolecule such as fetuin or ai-acid glycoprotein. Competition studies (Hudgin and Schachter, 1971a) have shown that the same enzyme or enzymes in pork liver...

A rapid procedure involving affinity chromatography on immobilized fetuin has been used to remove contaminating proteases from commercial preparations of neuraminidase. " The affinity-adsorbed enzyme was virtually free from protease activity, and the use of protease-free neuraminidase in studies of the metabolism of desialylized glycoproteins and of tumour cells was discussed. 

Oshiro, Y., and Eylar, E. H., 1968, Physical and chemical studies on glycoproteins. III. The microheterogeneity of fetuin, a fetal calf serum glycoprotein. Arch. Biochem. Biophys. 127 476-489. 

Spiro, R. G., 1960, Studies on fetuin, a glycoprotein of fetal serum I. Isolation, chemical composition, and physicochemical properties, J. Biol. Chem. 235 2860-2869. 

In studies with other systems, Glick et al. (1971) found sialidase, active toward fetuin, to be enriched in the lysosomal fraction of L cells Tulsiani and Carubelli (1971) found sialidase, active toward sialyllactose, not only enriched in lysomes isolated from rat mammary glands, but also in the soluble fraction Gielen et al. (1973) found a membrane-bound sialidase in leukocytes that was very active toward glycoproteins in the leukocyte homogenate and Bosmann (1974) found sialidase activity associated with the plasma membranes of human erythrocytes. Recently, Kishore et al. (1975) have reported the presence of a sialidase in Golgi isolated from rat liver. 

---