Ovotransferrins

Ouotransferrins. The peptide chain of hen ovotransferrin is identical to that of hen serotransferrin. However, both glycoproteins differ only by the structure of their glycans (see Figs. 16B,D). Two potential glycosylation sites have been identified 

Human lactotransferrin possesses three potential glycosylation sites (Asn-137, 478 and 624) and only two glycans in positions Asn-137 and Asn-478[74]. However, Van Berkel et al. [117] have identified a human lactotransferrin glycovariant glycosylated on Asn-624. 

Bovine lactotransferrin possesses five potential glycosylation sites, but the presence of only four glycans has been demonstrated and Asn-281 has not been glycosy- 

Caprine lactotransferrin has, like bovine lactotransferrin, five potential glycosylation sites (Fig. 4), but the location of glycans has not yet been defined. 

Porcine lactotransferrin possesses three potential iV-glycosylation sites which have been located in the C-terminal lobe (Asn-366, 472 and 571) (Fig. 4) [80] but only one site is glycosylated as recently demonstrated by Coddeville et al. [120]. 

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Ovoflavoprotein Ovoglycoprotein Ovoinhibitor Ovomacroglobulin Ovomucin Ovomucoid Ovotransferrin 150-Water Oxacephems Oxacillin [66-79-5]... 

Figure 5.1 Schematic diagram of the lactoferrin molecule. The positions of carbohydrate attachment are marked with a star. O, ovotransferrin T, human serotransferrin L, human lactoferrin R, rabbit serotransferrin M, melanotransferrin A, the connecting helix B, the C-terminal helix. The disulfide bridges are indicated by heavy bars, and the iron and carbonate binding sites by filled or open circles, respectively. Reprinted from Baker et al., 1987. Copyright (1987), with permission from Elsevier Science.

Isoelectric focusing of a mixture of proteins (1) soybean trypsin inhibitor (2) p-lactoglobulin A (3) p-iactoglobulin B (4) ovotransferrin (5) horse myoglobin (6) whale myoglobin and (7) cytochrome c. [Courtesy BioRaa Laboratories, Richmond, CA]... 

Milk transferrin (lactoferrin51a b c also found in leukocytes), hen egg transferrin (ovotransferrin),52 52a and rabbit and human serum transferrin54 543 all have similar structures. Each Fe3+ is bonded to oxygen anions from two tyrosine side chains, an aspartate carboxy-late, an imidazole group, and the bound carbonate ion (Fig. 16-2B). 

The transferrins are proteins that bind and transport iron as peIII 16-U.8 They indude lactoferrin from milk, ovotransferrin from egg white, and serum transferrin from a range of organisms. Uteroferrin, considered in Section 62.1.5.5.2 on the purple acid phosphatases, is an iron-binding protein with phosphatase activity, that has been proposed to transport iron from maternal to foetal circulation.824 826 There are distinct differences between the iron-binding sites in uteroferrin and transferrin, and so uteroferrin will not be discussed in this section. 

It appears that both halves of the transferrin molecule contain a recognition site for the receptor, and that both are necessary for binding. Thus, the two halves of ovotransferrin are much less effective than the whole molecule in binding to the receptor and donating iron into the chick embryo red blood cell.1143 One fragment of serum transferrin is ineffective.1124... 

Occasionally, the branchings are incomplete and the formation of the N-acetyl-lactosamine residues is only started in outline, as in the glycans of ovotransferrin (see Fig. 15), ovalbumin (see Fig. 16), and ovomucoid (see Fig. 18). In other instances, glycan structures such as have just been described are enriched with supplementary monosaccharide residues for example, the occurrence of disialyl groups [a-NeuAc-(2—>8)-a-NeuAc], and of /3-Gal-(l- 3) residues linked to the terminal galactosyl residues, has been demonstrated in different tissues and cell membranes,114,115 and in calf-thymocyte membranes,118 respectively. 

Ovotransferrin is also obtained from the white portion of a chicken egg and has been used as a chiral selector in liquid chromatography. This protein is also called conalbumin. It is a metal ion (iron, copper, manganese, and zinc) binding protein of molecular mass 70,000-78,000 and with an isoelectric point of 6.1-6.6. This protein is sensitive to acids and heat. 

Ovotransferrin Gal d3 12-13 76-78 6.0 686 2.6% Antimicrobial defense and iron-binding protein... 

Ibrahim, H.R. 1997. Insights into the structure-function relationships of ovalbumin, ovotransferrin, and lysozyme. In Hen Eggs Their Basic and Applied Science (T. Yamamoto, L.R. Juneja, H. Hatta, and M. Kim, eds), pp. 37-56. CRC Press, Boca Raton. 

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