Fetuin preparation

Fractionation of normal and immune sera immunoglobulins that react with fetuin Preparation of a protease-free preparation of neuraminidase... 

As mentioned in Section 11.2, a special class of proteinaceous targeting constructs are those in which a therapeutic protein is used as the active drug substance. In such a preparation, the protein is redirected to the target tissue by the attachment of site-directing ligands such as those discussed in Section 11.3. For instance, interferon beta (IFN- 3) can be redirected to the liver by enz5matic desialylation in a procedure similar to that described earlier for fetuin (Section 11.3.1). The resultant asialo-IFN- 3 was found to have an in vivo anti-viral effect when tested in a hepatitis B model in athymic nude mice [54]. 

Fetuin is a glycoprotein which has titratable groups associated with its carbohydrate moiety (sialic acid) in addition to those present on the protein. Spiro (1960) has determined the titration curve of the native protein, as well as that of a preparation from which sialic acid had been removed. The group count differed only in the number of groups assignable to sialic acid. In particular, the value of S was the same for both proteins. It is clear from these results that the combination of sialic acid with the protein does not involve any of the basic groups of the protein. 

SCHEME 15.20 Release of a tri-antennary complex type oligosaccharide from bovine fetuin allowed preparation of asparagine building block 172. 

Figure 33 An early glycan photoaffinity probe. This moiecuie was used to map gaiactose-binding sites on the asialoglycoprotein receptor. The probe was prepared from a desialylated fetuin glycopeptide galactose residues were modified with aryl azides (shown in red) and the peptide was labeled by radioiodination (shown in blue).

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... 

Dextran cyclic imidocarbonate derivatives have been prepared and used to immobilize phloretin, fetuin, and co-enzyme A. The co-enzyme was immobilized both by reaction with dextran cyclic imidocarbonate, and also via carbodi-imide-mediated coupling to 6-aminohexanoyl-dextran. y-Irradiation of dextran in the presence of trypsin, pepsin, or ribonuclease leads to production of active immobilized forms of these enzymes. ... 

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. 

---