Glycoproteins fetuin

Bayard investigated a number of glycoproteins (aracid glycoprotein, fetuin, lactotransferrin, transferrin, and ovomucoid) by N-deacetylation followed by deamination.176 They all gave the oligosaccharides 108 and 109, demonstrating the presence of common structural elements in these compounds. 

In 1998, Morten Meldal and coworkers demonstrated the semisynthesis of Asn derivatives of complex-type bi- and triantennary asialo N-glycans [58], After isolation of these oligosaccharides from the glycoproteins fetuin and ribonuclease (RNase) B by hydrazinolysis, the glycans were converted to Fmoc-Asn(oligosaccharide)-OH derivatives with an acetylated sugar part. In 2003, the Yasuhiro Kajihara group... 

Figure 11.25 Mass spectrometric sequencing of oligosaccharides. Carbohydrate-cleaving enzymes were used to release and specifically cleave the oligosaccharide component of the glycoprotein fetuin from bovine serum. Parts A and B show the masses obtained with MALDI-TOF spectrometry as well as the corresponding structures of the oligosaccharide-digestion products (using the same scheme as that in Figure 11.18) ...

It must be pointed out that the so-called quasi-albumins described by Poulik and Smithies (P13) are immunologically unrelated to albumin and would be more appropriately named quasi-oi-globulins. These proteins migrate just behind albumin in the vertical starch-gel electrophoretic technique of Smithies (S34) and include the group-specific (Gc) components. A fetal plasma protein of similar electrophoretic mobility is known (B12, B13), whose carbohydrate content is 23 mg/g, which clearly distinguishes it from the glycoprotein fetuin. Occasionally the protein persists and can be observed in some neonatal blood plasmas. 

White, H., Totty, N., Panayotou, G. (1993). Haemonectin, a granulocytic-cell-binding protein, is related to the plasma glycoprotein fetuin. Eur. J. Biochem. 213, 523-528. 

Incubation of sialyl substrates, such as a-1 acid glycoprotein, fetuin and sialyl lactose, with either live parasites or with preparations of lysed trypanosomes results in the release of sialic acid at an optimum pH of 6.0 to 6.5. Moreover, incubation of live trypomastigotes with human erythrocytes causes a time-dependent release of sialic acid from the erythrocyte surface. Similarly, the level of desialylation of erythrocytes from... 

Carbohydrate-cleaving enzymes were used to release and specifically cleave the oligosaccharide component of the glycoprotein fetuin from bovine serum. 

Hydrazinolysis, deamination, and methylation analysis have demonstrated that ai-acid glycoprotein, fetuin, lactotransferrin, and transferrin possess structural features in common. ... 

Spiro, R. G., 1964, Periodate oxidation of the glycoprotein fetuin, 7. Biol. Chem. 239 567. 

Neeser and Schweizer introduced 4 M CF3CO2H for 1 h at 121° for hydrolysis of glycoproteins. Both neutral and amino sugars were considered. They compared this method to hydrolysis with 0.6 M hydrochloric acid for 4 h at 100° and 3 M hydrochloric acid for 0.75 h at 125°. Hydrolysis of fetal-calf-serum fetuin, bovine submaxillary mucin, and horse-radish peroxidase showed hydrolysis with CF3CO2H to be superior. 

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... 

Figure 6. Effect of CMP-NeuAc concentration (V/S), of pH (V/pH), of enzymatic protein concentration (V/protein), and of incubation time (V/t) on the activity of synaptosomal membrane-bound sialyltransferase. Calf brain cortex. Acceptor substrates for sialyltransf erase (if) lactosylceramide ( ) desialylated fetuin (%) endogenous glycoprotein (endogenous glycolipids.

Kinetic Properties of Sialyltransferases. The sialyl-transferase activities with the endogenous glycoprotein and glycolipid acceptors in the standard assays (15) were linear with time for at least 60 min, while those with the exogenously added GMi and DS-fetuin were linear with time only for about 30 min (Figure 1). Activities were directly proportional to the amount of enzyme added up to 0.75 mg protein/assay (Figure 2). 

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). 

Figure 4. Effects of nonionic detergents on sialyltransferase activities. X. Endogenous glycoproteins A, exogenous DS-fetuin O, endogenous glycolipids O, exogenous GM, (16).

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