Transferrin properties

Strohmeier W (1968) Problem und Modell der homogenen Katalyse. 5 96-117 Sugiura Y, Nomoto K (1984) Phytosiderophores - Structures and Properties of Mugineic Acids and Their Metal Complexes. 58 107-135 Sun H, Cox MC, Li H, Sadler PJ (1997) Rationalisation of Binding to Transferrin Prediction of Metal-Protein Stability Constants. 88 71-102 Swann JC, see Bray RC (1972) II 107-144... 

Gutteridge, J.M.C. (1986). Antioxidant properties of the proteins caeruloplasmin, albumin and transferrin. A study of their activity in serum and synovial fluid fiom patients with rheumatoid arthritis. Biochim. Biophys. Acta 869, 119-127. 

A synthetic peptide has been designed to mimic the effects of viral fusogenic properties (114,115). It consists of 30 amino acids with the major repeat of Glu-Ala-Leu-Ala so, it is referred to as a GALA peptide. It undergoes a conversion from an aperiodic conformation at neutral pH and becomes an amphipathic alpha helix at pH 5. In the more acidic environment, the peptide interacts with lipid bilayers (114,115). GALA has been incorporated into transferrin-targeted liposome, with the effect of significantly... 

Figure 14-12 Spectroscopic measurement of log [Fe(lll)Trfc]/[Fe(ll)Trfc] versus potential at pH 5.8. [S. Dhungana. C. H. Taboy, O. Zak, M. Larvie. A L Crumbliss, and RAisen, Redox Properties of Human Transferrin Bound to Its Receptor,Biochemistry, 2004, 43,205.]...

Investigations of the kinetics of the reaction of these new siderophores with iron-saturated transferrin showed a rapid formation of a ternary complex with transferrin, followed by a slow step in which the ferric siderophore was released from the apoprotein. Weitl et al.257 have evaluated the ferric-chelating properties of several of these siderophores and found the following order of effectiveness for removing iron from transferrin enterobactin > MECAMS > MECAM > LICAMS > DFOA > TRIM-CAMS. 

Chemists have a variety of different interests in the transferrins. One interest concerns the chemistry of the binding of metal ions. No prosthetic or unusual chemical groupings are present in the proteins, and the binding is rather a property of the unique folding and juxtaposition of the normal chemical groupings in protein molecules (49). Another interest is in the mechanism of the release of iron by the serum transferrin to the tissues. The iron is so tightly bound that some investigators have attempted to invoke a special enzymatic mechanism for the dissociation in the tissues, but no evidence for this has been found. 

The iron-binding protein of serum transferrin was found in fraction IV-3,4 of human plasma when the plasma was fractionated by low temperature ethanol fractionation procedures (31, 116). By further subfractionations, serum transferrin could be concentrated in Cohn fraction IV-7 (30, 125, 126). Cohn (30) first reported the properties of the isolated protein, which he called the 3i metal-binding protein since the protein had been found to bind copper, and possibly zinc, as well as iron. Holm-berg and Laurell (66) proposed that the protein be called transferrin on the basis that the principal function of the protein was associated with the transport of iron in serum and that it was not the major copperbinding protein in human serum. 

Although the transferrins occur in three major biological fluids, blood serum, milk and avian egg whites, only the function of the blood serum transferrin apparently has been described satisfactorily. There appears to be little question that the main function of blood serum transferrin is the transport of iron (72, 99, 114). Another much less recognized property of... 

A function of ovotransferrin in the avian egg has not been demonstrated. As attractive as is the concept of a function for transferrin during embryonic development, essentially all the iron of the egg is in the yolk and during embryonic development the main fate of the egg white appears to be as a source of food for the embryo (61). However, there is so very little known about the breakdown and resynthesis of protein and other substances during embryo development in the avian egg, the iron binding property of the transferrin might have a yet unrecognized function. 

The methods that have been used in the preparation of the various transferrins include most of those generally used in the preparation of proteins. In addition, the particular properties of the iron complexes have been used for the development of adjunctive procedures. The iron complexes have solubilities that differ from those of the metal-free proteins, and the iron complexes are relatively stable proteins as compared to most other proteins. The stability of the iron complex can be used to denature and insolubilize preferentially other proteins present as contaminants. 

The values for the N-terminal amino acids of five different transferrins are given in Table 6. Three out of the five have been reported to have alanine. The absence of an N-terminal amino acid in human lactotrans-ferrin (95) is an unexpected finding in view of the many physical and chemical properties human lactotransferrin and other transferrins have in common (22, 137). Confirmation of this absence is highly desirable. 

The metal-free proteins do not exhibit any physical properties which are not common to other globular proteins of medium molecular size. In fact, the first transferrin studied, chicken ovotransferrin, was considered for many years to be a rather nondescript egg-white protein. There are several striking changes in the physical properties of transferrins upon chelation of metal ions, but most of these properties are so similar to those of the metal-free protein that many of the physical studies have not been useful in attempting to understand the mechanism of metal binding. Several important exceptions will be described in a subsequent section. 

Extensive studies have been made of the charge relationships and electrostatic properties of ovotransferrin, and a few studies have been made on other transferrins. Several of these primarily concern the changes seen on chelation of metal ions, which will be discussed below. Most of the transferrins have isoelectric points around pH 6 (Fig. 2), but the isoelectric point may vary considerably with species and may show taxonomic relationships (28). These will be discussed below under genetic relationships. 

V. Comparative Properties of the Metal-Free and Metal Complexes of Transferrins... 

With but few exceptions, definitive studies on the properties of the metal complexes have been done with human serum transferrin and chicken ovotransferrin, the majority having been done with the chicken ovotransferrin. Many of the properties of the metal complexes are very similar to, if not identical with, those of the metal-free proteins but also there are several rather distinctive differences. 

Fiala (45) and Fiala and Burk (46) early postulated, by analogy from the visible absorption spectra of iron transferrin and the iron complex of aspergillic acid, that iron was bound in transferrins through a hydroxamic acid-CC>2 complex. This formulation is shown in Fig. 15. Fraenkel-Conrat (48), however, could find no evidence for hydroxylamido groups in chicken ovotransferrin. He also prepared and studied the properties of several hydroxylamido proteins by the chemical introduction of the hydroxylamido groups, and found that their properties were quite different from those of the transferrins. 

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