1
|
Rashid AM. The location of structural difference between ovotransferrin types A and B in hens. ANIMAL BLOOD GROUPS AND BIOCHEMICAL GENETICS 2009; 12:241-8. [PMID: 7342800 DOI: 10.1111/j.1365-2052.1981.tb01557.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
A comparison of ovotransferrin types A and B showed that in starch gel electrophoresis both types consisted of one major and one minor component. Both types have a similar amino acid composition as do the fragments from each type. Starch gel electrophoresis shows that the cause of the difference in the electrophoretic mobilities between ovotransferrin types A and B lies in the C-terminal half of the molecule. No physiological difference was found between types A and B, both types donate iron to chicken embryo red cells at equal rate.
Collapse
|
2
|
Ko KY, Ahn DU. An economic and simple purification procedure for the large-scale production of ovotransferrin from egg white. Poult Sci 2008; 87:1441-50. [PMID: 18577628 DOI: 10.3382/ps.2007-00434] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The objective of this study was to develop a simple and economical protocol for separating ovotransferrin from egg white. Egg white was separated from the yolk and diluted with the same volume of distilled water. To prevent denaturation during the separation process, ovotransferrin in 2x-diluted egg white was converted to its holo-form by adding 20 mM FeCl3.6H2O solution (0.25 to 3 mL/100 mL). The pH of egg white was adjusted to pH 7.0, 8.0, or 9.0, and NaHCO3 and NaCl were added to 50 mM and 0.15 M, respectively (final concentrations) to facilitate iron binding to ovotransferrin. The iron-bound ovotransferrin was separated from the egg white using different concentrations of ethanol (30 to 50%). Ethanol at 43% (final concentration) and pH at 9.0 were the best conditions for separating iron-bound ovotransferrin from 2x-diluted egg white solution. Almost all egg white proteins including ovalbumin were precipitated at 43% ethanol, but most of the iron-bound ovotransferrin remained in the supernatant. Holo-ovotransferrin in the 43% ethanol solution started to precipitate as the concentration of ethanol increased, but the optimal condition for precipitating ovotransferrin was when the ethanol concentration reached 59% (final). The precipitated holo-ovotransferrin was dissolved with distilled water, and AG1-X(2) ion exchange resin (at 3x iron content in ovotransferrin) was used to remove iron bound to ovotransferrin after pH adjustment to 4.7 using 500 mM citric acid. The apo-ovotransferrin obtained using this protocol was >80% in purity and around 99% in yield. The protocol developed is simple, economical, and appropriate for a large-scale production of ovotransferrin from egg white. Also, the isolated ovotransferrin can be applied in human foods, because the only solvent used in this process is ethanol. Furthermore, the AG1-X2 ion exchange resin and ethanol used in this process can be regenerated and recovered.
Collapse
Affiliation(s)
- K Y Ko
- Department of Animal Science, Iowa State University, Ames, Iowa 50011-3150, USA
| | | |
Collapse
|
3
|
Boffi F, Ascone I, Della Longa S, Girasole M, Yalovega G, Soldatov AV, Varoli-Piazza A, Congiu Castellano A. X-ray absorption near-edge spectroscopy of transferrins: a theoretical and experimental probe of the metal site local structure. EUROPEAN BIOPHYSICS JOURNAL : EBJ 2003; 32:329-41. [PMID: 12851791 DOI: 10.1007/s00249-003-0283-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2002] [Revised: 12/17/2002] [Accepted: 12/19/2002] [Indexed: 11/24/2022]
Abstract
Proteins of the transferrin (Tf) family have a role in metal transport in vertebrates and have been extensively studied. The results here reported provide, for the first time, a detailed systematic comparison of metal sites in Tf complexes involving several atoms in the whole protein and in two different types of Tfs. The high interest in the structural variations induced in a metalloprotein upon the uptake of different metals is related to the hypothesis of the metals' involvement in some neuropathologies. We propose a comparative study of the X-ray absorption spectra at the K-edge of iron, copper, zinc and nickel in serotransferrin and ovotransferrin. The experimental data are simulated using an algorithm of the full multiple scattering method. Our results show that: (1) the local structure of each site (N-terminal and C-terminal) is correlated to the ligation state of the other site; (2) the difference between the two proteins is related to site local structure and depends on the metal ion nature being greater in the case of copper and zinc with respect to iron and nickel ions; (3) X-ray spectroscopy is confirmed as a suitable technique able to discriminate between coordination models proposed by X-ray diffraction.
Collapse
Affiliation(s)
- F Boffi
- Dipartimento di Fisica and INFM, Università La Sapienza, Piazzale A. Moro 2, 00185 Rome, Italy
| | | | | | | | | | | | | | | |
Collapse
|
4
|
|
5
|
|
6
|
Regoeczi E, Chindemi PA, Hu WL. Interaction of transferrin and its iron-binding fragments with heparin. Biochem J 1994; 299 ( Pt 3):819-23. [PMID: 8192672 PMCID: PMC1138094 DOI: 10.1042/bj2990819] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The interaction of heparin with transferrin (Tf; bovine and rat) and the isolated iron-binding lobes of bovine Tf were investigated. Affinity chromatography of rat Tf on heparin-agarose showed that interaction depended on both the iron content of Tf and the pH of the medium. Both the iron-free and iron-saturated forms of Tf were strongly bound by the column at pH 5.6, but only the iron-free form revealed significant affinity at pH 7.4. Desialylation of Tf moderately promoted interaction, treatment with cyclohexanedione moderately reduced interaction, and succinylation abolished it altogether. In the presence of heparin, iron release from the N-terminal lobe of native bovine Tf was accelerated and from the C-terminal lobe it was slightly reduced. The heparin effect remained qualitatively the same on each lobe after their separation by tryptic digestion and DEAE-cellulose chromatography. The affinity of native bovine Tf for heparin was very close to that of its isolated N-terminal lobe, thus suggesting that it is this portion of the molecule that binds to the glycosaminoglycan. It is concluded that the consequences for iron-binding strength of the two transferrin lobes are diagonally opposite when Tf is bound to heparin as opposed to its natural cell-surface receptor.
Collapse
Affiliation(s)
- E Regoeczi
- Department of Pathology, McMaster University Health Sciences Centre, Hamilton, Ontario, Canada
| | | | | |
Collapse
|
7
|
|
8
|
Garratt RC, Evans RW, Hasnain SS, Lindley PF, Sarra R. X.a.f.s. studies of chicken dicupric ovotransferrin. Biochem J 1991; 280 ( Pt 1):151-5. [PMID: 1660264 PMCID: PMC1130613 DOI: 10.1042/bj2800151] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
A comparison of Cu K-edge x.a.f.s. spectra with that of the equivalent Fe K-edge for chicken ovotransferrin (COT) indicates that the metal ions occupy essentially the same binding sites in the protein. However, in the case of the Cu2+ complex the metal appears to have reduced co-ordination. Changes are observed in the x.a.f.s. of 90%-saturated COT (Cu1.8COT) on freeze-drying. The three-dimensional X-ray structures of rabbit serum transferrin and human lactoferrin have shown that the ferric cations are co-ordinated by four protein ligands and a bidentate carbonate anion in a distorted octahedral arrangement [Anderson, Baker, Dodson, Norris, Rumball, Waters & Baker (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 1768-1774; Anderson, Baker, Norris, Rice and Baker (1989) J. Mol. Biol. 209, 711-734; Bailey, Evans, Garratt, Gorinsky, Hasnain, Horsburgh, Jhoti, Lindley, Mydin, Sarra & Watson (1988) Biochemistry 27, 5804-5812]. This structural information, together with the differences in e.x.a.f.s. spectra for solution and freeze-dried samples of diferric COT [Hasnain, Evans, Garratt & Lindley (1987) Biochem. J. 247, 369-375] suggests that the synergistic carbonate anion may be capable of behaving as a unidentate linkage to the Cu2+ in the dicupric complex. Data for Cu1.8COT are consistent with only three protein ligands bound to Cu2+, monodentate binding of the synergistic anion in one lobe and its bidentate binding in the other lobe. Such flexibility in the anion co-ordination may be a requirement for the uptake and release of metals by the transferrins.
Collapse
Affiliation(s)
- R C Garratt
- Molecular Biophysics Group, Daresbury Laboratory, Warrington, Cheshire, U.K
| | | | | | | | | |
Collapse
|
9
|
Abstract
The chemistry and molecular biology of transferrin is discussed. The discussion covers the genetic control of transferrin synthesis, its intracellular synthesis, intra- and extracellular transport, and its interaction with transferrin receptors. The role of transferrin in iron metabolism is evaluated, both with regard to iron uptake by transferrin as to iron uptake from transferrin by different cells. The knowledge on the biochemical mechanisms involved in iron uptake is presented, with special reference to the triple role of the acidification of endocytotic vesicles. Apart from its traditional role in iron metabolism, transferrin acts as a growth factor. A distinction of two groups of growth-stimulating properties of transferrin has been made. As an early effect, membranous and intracellular changes are initiated, possibly based on electrochemical effects on the cell. The late effects seem to relate to its role in iron transport. Interestingly, the early growth stimulating effects can be segregated from the former function of transferrin and strictly speaking neither depend on iron nor on the transferrin molecule itself. Also the trophic effect of transferrin on several cell types has been described. Hypotheses concerning the biochemical basis of this effect are presented and within this context a new hypothesis on the differential occupation of iron binding sites of serum transferrin is forwarded. Examples of the applicability of present understanding of the biology of transferrin in clinical settings are presented.
Collapse
Affiliation(s)
- G de Jong
- Department of Chemical Pathology, Erasmus University Rotterdam, The Netherlands
| | | | | |
Collapse
|
10
|
Rochard E, Legrand D, Mazurier J, Montreuil J, Spik G. The N-terminal domain I of human lactotransferrin binds specifically to phytohemagglutinin-stimulated peripheral blood human lymphocyte receptors. FEBS Lett 1989; 255:201-4. [PMID: 2551729 DOI: 10.1016/0014-5793(89)81091-9] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Human lactotransferrin receptors have been recently characterized on mitogen-stimulated human lymphocytes [(1989) Eur. J. Biochem. 179, 481-487]. In order to define the lactotransferrin recognition site by these receptors, the binding to lymphocytes of several tryptic fragments, isolated from human lactotransferrin by mild tryptic hydrolysis [(1984) Biochim. Biophys. Acta 787, 90-96], has been investigated. The 30 kDa N-tryptic fragment (residues 4-281) and the re-associated N,C-tryptic complex bind to lactotansferrin lymphocyte receptor with a dissociation constant of 44 nM and 39 nM, respectively, similar to the value obtained for the native lactotransferrin (Kd = 46 nM). However, neither the N-terminal domain II (residues 91-257) nor the 50 kDa C-tryptic fragment (residues 282-703) are recognized. These results suggest that the binding site of human lactotransferrin by the lymphocyte receptor is located in the N-terminal lobe and more precisely in the N-terminal domain I (residues 4-90 and/or 258-281).
Collapse
Affiliation(s)
- E Rochard
- Laboratoire de Chimie Biologique, CNRS no. 111, Université des Sciences et Techniques de Lille Flandres-Artois, Villeneuve d'Ascq, France
| | | | | | | | | |
Collapse
|
11
|
de Jong G, van Eijk HG. Functional properties of the carbohydrate moiety of human transferrin. THE INTERNATIONAL JOURNAL OF BIOCHEMISTRY 1989; 21:253-63. [PMID: 2663561 DOI: 10.1016/0020-711x(89)90183-3] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- G de Jong
- Department of Chemical Pathology, Medical Faculty, Erasmus University Rotterdam, The Netherlands
| | | |
Collapse
|
12
|
Church WR, Brown SA, Mason AB. Monoclonal antibodies to the amino- and carboxyl-terminal domains of ovotransferrin. Hybridoma (Larchmt) 1988; 7:471-84. [PMID: 2461899 DOI: 10.1089/hyb.1988.7.471] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Monoclonal antibodies to the iron transport protein ovotransferrin were produced by immunizing mice simultaneously with ovotransferrin and with the proteolytically derived amino- and carboxyl-terminal half-molecule domains of ovotransferrin. Two isolated hybridoma clones (designated alpha OT + N1 and alpha OT + N2) produced antibodies (IgG1) to determinants located on holo-ovotransferrin and the amino-terminal domain; two hybridoma clones (designated alpha OT + C1 and alpha OT + C2) produced antibodies (IgG1) to determinants on holo-ovotransferrin and the carboxyl-terminal domain. One hybridoma clone (designated alpha OT-N1) produced an antibody (IgG1) that bound only the amino-terminal domain and did not bind holo-ovotransferrin. Both alpha OT + N1, and alpha OT-N1 bound to antigen less tightly after removal of iron; antibodies alpha OT + N2, alpha OT + Cl, and alpha OT + C2 were unaffected by removal of iron from holo-ovotransferrin or the isolated domains. Intact disulfide bonds in the antigens were required for binding by the antibodies. These antibodies should prove useful as probes for discrete regions of the ovotransferrin molecule, in particular, those regions involved in binding to the transferrin receptor.
Collapse
Affiliation(s)
- W R Church
- Department of Biochemistry, University of Vermont, College of Medicine, Burlington 05405
| | | | | |
Collapse
|
13
|
de Jong G, van Eijk HG. Microheterogeneity of human serum transferrin: a biological phenomenon studied by isoelectric focusing in immobilized pH gradients. Electrophoresis 1988; 9:589-98. [PMID: 3243256 DOI: 10.1002/elps.1150090921] [Citation(s) in RCA: 101] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The heterogeneity of human transferrin results from (i) differences in iron content, (ii) genetic polymorphism and (iii) differences in the carbohydrate moiety. This article primarily deals with the last phenomenon, the microheterogeneity of human transferrin. Owing to the comparatively simple carbohydrate structure of human transferrin and the high resolving power of isoelectric focusing in immobilized pH gradients, microheterogeneous forms of transferrin can be separated. Differences between samples can be quantitated by crossed immunoelectrophoresis. Examples of the differences between the microheterogeneity patterns of transferrin in several biological fluids and the changes that can be observed in diseases such as rheumatoid arthritis, idiopathic hemochromatosis and Kahler's disease are presented. Special attention has been focused on changes occurring during pregnancy.
Collapse
Affiliation(s)
- G de Jong
- Department of Chemical Pathology, Medical Faculty, Erasmus University, Rotterdam, The Netherlands
| | | |
Collapse
|
14
|
Legrand D, Mazurier J, Montreuil J, Spik G. Structure and spatial conformation of the iron-binding sites of transferrins. Biochimie 1988; 70:1185-95. [PMID: 3147711 DOI: 10.1016/0300-9084(88)90184-8] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Transferrins are iron-binding glycoproteins involved in iron metabolism and antibacterial defense mechanisms. Since the discovery of transferrins, many studies have attempted to characterize the iron ligands and to establish the conformation of the iron-binding sites. From chemical and spectroscopic studies, it was generally accepted that iron was hexacoordinated to Tyr and His residues, to a water molecule and to a (bi)carbonate ion, electrostatically linked to an Arg residue. On the basis of these studies, on the one hand, and on the basis of the homologies between the amino acid sequences of transferrins, on the other hand, predicted data have been provided about the number and location of the iron ligands. Recent X-ray crystallography studies of human lactotransferrin have partially confirmed the above-mentioned predicted data and have brought invaluable information about the nature of the ligands and the conformation of the iron-binding site. On the basis of the obtained results, a scheme has been proposed in which the iron is coordinated to 2 Tyr, 1 His and 1 Asp residues, to a (bi)carbonate linked to an Arg residue and probably to a water molecule. The iron-binding site is located at the interface between the two domains which constitute each lobe of the transferrins.
Collapse
Affiliation(s)
- D Legrand
- Laboratoire de Chimie Biologique (CNRS UA217, Université des Sciences et Techniques de Lille Flandres-Artois, Villeneuve-d'Aseq, France
| | | | | | | |
Collapse
|
15
|
Abstract
Partial proteolysis was used to prepare half-molecule fragments of hen ovotransferrin. N-Terminal and C-terminal fragments associate to form an N-terminal fragment-C-terminal fragment dimer. Variant forms of the N- and C-terminal fragments can be prepared in which a few amino acid residues are lacking from the C-terminal ends of the fragments. These variant fragments are partially or completely unable to associate; the suggestion that the molecular recognition sites are located in these C-terminal stretches of the N-terminal half-molecule (320-332) and of the C-terminal half-molecule (683-686) is in agreement with X-ray-crystallography data for human lactotransferrin [Anderson, Baker, Dodson, Norris, Rumball, Waters & Baker (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 1769-1773].
Collapse
Affiliation(s)
- J Williams
- Department of Biochemistry, University of Bristol, U.K
| | | |
Collapse
|
16
|
Mason AB, Brown SA, Church WR. Domain-specific monoclonal antibodies to ovotransferrin indicate conservation of determinants involved in avian transferrin receptor recognition. COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY. B, COMPARATIVE BIOCHEMISTRY 1988; 91:541-9. [PMID: 2466604 DOI: 10.1016/0305-0491(88)90019-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
1. Three of five monoclonal antibodies produced to chicken ovotransferrin bound quail ovotransferrin but none of the antibodies bound human, bovine or equine serum transferrin. 2. Equilibrium binding experiments indicate that both quail and chicken ovotransferrin bind to transferrin receptors on chick reticulocytes although the quail protein binds to 40% fewer sites with an affinity which is three times lower than chicken ovotransferrin. 3. The antibodies that recognize quail ovotransferrin block binding of both radiolabelled chicken and quail ovotransferrin to chick reticulocytes. 4. Quail NH2-terminal half-molecule domain appears to be unable to form a functional hybrid holo-ovotransferrin with chicken C-terminal half-molecule domain.
Collapse
Affiliation(s)
- A B Mason
- Department of Biochemistry, University of Vermont College of Medicine, Burlington 05405
| | | | | |
Collapse
|
17
|
Monoclonal antibodies to either domain of ovotransferrin block binding to transferrin receptors on chick reticulocytes. J Biol Chem 1987. [DOI: 10.1016/s0021-9258(18)48038-6] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
|
18
|
Cheuk MS, Loh TT, Hui YV, Keung WM. Kinetics of pyrophosphate induced iron release from diferric ovotransferrin. J Inorg Biochem 1987; 29:301-11. [PMID: 3035088 DOI: 10.1016/0162-0134(87)80036-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The kinetics of pyrophosphate-induced iron release from diferric ovotransferrin were studied spectrophotometrically at 37 degrees C in 0.1 M HEPES, pH 7.0. At high pyrophosphate concentrations, the kinetics are biphasic, indicating that the rates of iron release from the two, presumably noninteracting iron-binding sites of ovotransferrin are different. The pseudo-first-order rate constants for iron release from both the fast and slow sites exhibit a hyperbolic dependence on pyrophosphate concentrations. The data suggest that pyrophosphate forms complexes with the two iron-binding sites of ovotransferrin prior to iron removal. The stability constants of the complex formed with the fast site (Keqf) and slow site (Keqs) are 8.3 M-1 and 40.4 M-1, respectively. The first-order rate constants for the dissociation of ferric-pyrophosphate from the fast site (k2f) and the slow site (k2s) are 0.062 and 0.0044 min-1, respectively. Results from urea gel electrophoresis studies suggest that iron is released at a much faster rate from the N-terminal binding site of ovotransferrin. At high pyrophosphate concentration, only C-monoferric-ovotransferrin is detected during the course of iron release. At low pyrophosphate concentration, however, a detectable amount of N-monoferric-ovotransferrin is accumulated. This result is consistent with the kinetic finding that the site with a higher k2 (0.062 min-1) has a lower affinity toward pyrophosphate (Keq = 8.3 M-1) whereas the site with a lower k2 (0.0044 min-1) has a higher affinity for pyrophosphate (Keq = 40.4 M-1).
Collapse
|
19
|
Abstract
An iron-containing fragment (Mr approximately 39,000) of rabbit serum transferrin has been crystallized from a solution of 25% (w/v) polyethylene glycol 6000, 50 mM-disodium piperazine-N,N'bis(2-ethanesulphonate) adjusted to pH 6.0 at 4 degrees C. The space group is P3(1)21 (or the enantiomorph) with a = b = 66.8(1) A, c = 137.5(3) A and Z = 6. The crystals appear as hexagonal plates, with the unique axis perpendicular to the plate. The crystals, kept at 4 degrees C, are stable in the X-ray beam for at least 130 hours and diffract to better than 1.8 A resolution.
Collapse
|
20
|
Williams J, Moreton K, Goodearl AD. Selective reduction of a disulphide bridge in hen ovotransferrin. Biochem J 1985; 228:661-5. [PMID: 4026802 PMCID: PMC1145035 DOI: 10.1042/bj2280661] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Brief treatment of iron-saturated hen ovotransferrin with dithiothreitol selectively cleaves the disulphide bridge between residues 478 and 671, which is in the C-terminal domain of the protein. The reduced alkylated protein is less stable than the native protein, and its iron-binding properties are different. A fluorescent derivative was prepared by coupling N-iodoacetyl-N'-(5-sulpho-1-naphthyl)ethylenediamine to the thiol groups.
Collapse
|
21
|
Metz-Boutigue MH, Jollès J, Mazurier J, Schoentgen F, Legrand D, Spik G, Montreuil J, Jollès P. Human lactotransferrin: amino acid sequence and structural comparisons with other transferrins. EUROPEAN JOURNAL OF BIOCHEMISTRY 1984; 145:659-76. [PMID: 6510420 DOI: 10.1111/j.1432-1033.1984.tb08607.x] [Citation(s) in RCA: 369] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
The complete amino acid sequence (703 amino acid residues) of human lactotransferrin has been determined. The location of the disulfide bridges has also been investigated. Computer analysis established internal homology of the two domains (residues 1-338 and residues 339-703). Each domain contains a single iron-binding site and a single glycosylation site (asparagine residues 137 and 490) located in homologous positions. Prediction of the secondary structure of the two homologous moieties of human lactotransferrin has also been performed. The present results allowed a series of comparisons to be made with human serum transferrin and hen ovotransferrin.
Collapse
|
22
|
Legrand D, Mazurier J, Metz-Boutigue MH, Jolles J, Jolles P, Montreuil J, Spik G. Characterization and localization of an iron-binding 18-kDa glycopeptide isolated from the N-terminal half of human lactotransferrin. BIOCHIMICA ET BIOPHYSICA ACTA 1984; 787:90-6. [PMID: 6722176 DOI: 10.1016/0167-4838(84)90111-0] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Mild treatment of iron-saturated human lactotransferrin by trypsin at pH 8.2 cleaves the molecule into a N-tryptic (Mr approximately equal to 30000) and a C-tryptic (Mr approximately equal to 50000) fragment, which have been isolated. Each of them carries a glycan moiety and keeps the property to bind reversibly one Fe3+. The N-tryptic fragment has been submitted to a second tryptic digestion which led to an iron-binding glycopeptide fragment with a molecular weight of about 18500. This fragment, the smallest iron-binding peptide isolated up to now from a transferrin, includes the ND2 domain of human lactotransferrin.
Collapse
|
23
|
Yamamura T, Hagiwara S, Nakazato K, Satake K. Copper complexes at N- and C-site of ovotransferrin: quantitative determination and visible absorption spectrum of each complex. Biochem Biophys Res Commun 1984; 119:298-304. [PMID: 6422937 DOI: 10.1016/0006-291x(84)91651-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Copper complexes at the two sites of ovotransferrin (TF) differed markedly in the rate of Cu release by EDTA. During the reaction, lambda max of the remaining Cu-Tf complex shifted to red side, while the difference spectrum of FenCu2-nTf vs. FenTf in which the N-site had been preferentially occupied with Fe had lambda max at blue side from that of Cu2Tf, 440 nm. From these results, the intrinsic spectrum for Cu-complex at each site was assigned: lambda max 450 nm for N- and 430 nm for C-site. The differences in the release rate and the spectrum can be used for the identification of the two domains of Tf and for the analysis of metal-binding behavior of each site.
Collapse
|
24
|
Brown-Mason A, Woodworth RC. Physiological levels of binding and iron donation by complementary half-molecules of ovotransferrin to transferrin receptors of chick reticulocytes. J Biol Chem 1984. [DOI: 10.1016/s0021-9258(17)43488-0] [Citation(s) in RCA: 33] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
|
25
|
Transferrins in the metabolism of iron. Chem Nat Compd 1984. [DOI: 10.1007/bf00579469] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
|
26
|
MacGillivray RT, Mendez E, Shewale JG, Sinha SK, Lineback-Zins J, Brew K. The primary structure of human serum transferrin. The structures of seven cyanogen bromide fragments and the assembly of the complete structure. J Biol Chem 1983. [DOI: 10.1016/s0021-9258(18)32696-6] [Citation(s) in RCA: 208] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
|
27
|
Heaphy S, Williams J. The preparation and partial characterization of N-terminal and C-terminal iron-binding fragments from rabbit serum transferrin. Biochem J 1982; 205:611-7. [PMID: 6816218 PMCID: PMC1158528 DOI: 10.1042/bj2050611] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Two iron-binding fragments of Mr 36 000 and 33 000 corresponding to the N-terminal domain of rabbit serum transferrin were prepared. One iron-binding fragment of Mr 39 000 corresponding to the C-terminal domain was prepared. The N-terminal amino acid sequence of rabbit serum transferrin is: Val-Thr-Glu-Lys-Thr-Val-Asn-Trp-?-Ala-Val-Ser. One glycan unit is presented in rabbit serum transferrin and it is located in the C-terminal domain.
Collapse
|
28
|
MacGillivray RT, Mendez E, Sinha SK, Sutton MR, Lineback-Zins J, Brew K. The complete amino acid sequence of human serum transferrin. Proc Natl Acad Sci U S A 1982; 79:2504-8. [PMID: 6953407 PMCID: PMC346227 DOI: 10.1073/pnas.79.8.2504] [Citation(s) in RCA: 113] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
The complete amino acid sequence of human serum transferrin has been determined by aligning the structures of the 10 CNBr fragments. The order of these fragments in the polypeptide chain is deduced from the structures of peptides overlapping methionine residues and other evidence. Human transferrin contains 678 amino acid residues and--including the two asparagine-linked glycans--has an overall molecular weight of 79,550. The polypeptide chain contains two homologous domains consisting of residues 1-336 and 337-678, in which 40% of the residues are identical when aligned by inserting gaps at appropriate positions. Disulfide bond arrangements indicate that there are seven residues between the last half-cystine in the first domain and the first half-cystine in the second domain and therefore, a maximum of seven residues in the region of polypeptide between the two domains. Transferrin--which contains two Fe-binding sites--has clearly evolved by the contiguous duplication of the structural gene for an ancestral protein that had a single Fe-binding site and contained approximately 340 amino acid residues. The two domains show some interesting differences including the presence of both N-linked glycan moieties in the COOH-terminal domain at positions 413 and 610 and the presence of more disulfide bonds in the COOH-terminal domain (11 compared to 8). The locations of residues that may function in Fe-binding are discussed.
Collapse
|
29
|
Keung W, Azari P, Phillips J. Structure and function of ovotransferrin. I. Production of iron-binding fragments from iron-ovotransferrin by the action of immobilized subtilisin. Purification and characterization of the fragments. J Biol Chem 1982. [DOI: 10.1016/s0021-9258(19)68171-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
|
30
|
Williams J, Elleman TC, Kingston IB, Wilkins AG, Kuhn KA. The primary structure of hen ovotransferrin. EUROPEAN JOURNAL OF BIOCHEMISTRY 1982; 122:297-303. [PMID: 6895872 DOI: 10.1111/j.1432-1033.1982.tb05880.x] [Citation(s) in RCA: 164] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Peptide sequences obtained from hen ovotransferrin are compared with the complete amino acid sequence of the protein deduced from a cDNA sequence (Jeltsch and Chambon, preceding paper). Of the 705 positions of the whole protein 605 can be matched by the peptide sequences. Some possible discrepancies between the two methods are pointed out. The two halves of the chain show marked similarities in their sequences with 37% identical residues. The positions of the 15 disulphide bridges are shown; there are 6 homologous bridges in each half of the molecule and 3 extra bridges which occur only in the C-terminal half. The terminal residues of the half-molecule fragments obtained by limited proteolysis are identified. The two domains are joined by a 9-residue connecting peptide. Sequence variability has been found at 9 positions. The sequence of hen ovotransferrin is compared with the partial available for human transferrin. From this some tentative conclusions about the identities of the metal-binding residues and about the evolution of transferrin are reached.
Collapse
|
31
|
Williams J, Grace SA, Williams JM. Evolutionary significance of the renal excretion of transferrin half-molecule fragments. Biochem J 1982; 201:417-9. [PMID: 6805466 PMCID: PMC1163659 DOI: 10.1042/bj2010417] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
It is generally thought that the duplicated structure of serum transferrin in vertebrates arose by gene duplication and fusion from a small ancestral protein. We have found that the isolated domains of transferrin are rapidly lost from the bloodstream via the kidneys. Therefore we suggest that the ancestral transferrin was not a serum protein or, alternatively, that it was not as small as the half-molecule.
Collapse
|
32
|
Keung W, Azari P. Structure and function of ovotransferrin. II. Iron-transferring activity of iron-binding fragments of ovotransferrin with chicken embryo red cells. J Biol Chem 1982. [DOI: 10.1016/s0021-9258(19)68172-x] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
|
33
|
Kannagi R, Koizumi K, Masuda T. Limited hydrolysis of platelet membrane phospholipids. On the proposed phospholipase-susceptible domain in platelet membranes. J Biol Chem 1981. [DOI: 10.1016/s0021-9258(19)69946-1] [Citation(s) in RCA: 58] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
|
34
|
|
35
|
Esparza I, Brock JH. The interaction of bovine transferrin and monoferric transferrin fragments with rabbit reticulocytes. BIOCHIMICA ET BIOPHYSICA ACTA 1980; 624:479-89. [PMID: 7417489 DOI: 10.1016/0005-2795(80)90089-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
1. The mechanism of interaction of transferrin with reticulocytes has been investigated using monoferric fragments derived by proteolysis from bovine Fe2-transferrin. 2. Rabbit reticulocytes readily took up iron from bovine transferrin, but only slight uptake occurred from the C-terminal fragment (S), and almost none from the N-terminal fragment (F). 3. The degree of binding of transferrin and fragments to the cells was in the order transferrin greater than fragment F greater than fragment S. 4. Binding of transferrin and fragment S, but not of fragment F, was reduced when incubation was performed at 4 degrees C instead of 37 degrees C, and all iron uptake was abolisehd. 5. Preincubation of reticulocytes with fragment S, but not with fragment F, somewhat reduced subsequent iron uptake from transferrin. 6. The presence of bovine serum albumin (40 mg/ml) in the incubation buffer inhibited iron uptake, but iron uptake nevertheless occurred from transferrin in bovine serum. 7. No differences were detected in the rate of 59Fe uptake from transferrin labelled asymmetrically by sequential additions of 59Fe and 56Fe to apotransferrin. 8. It is concluded that both halves of the transferrin molecule are involved, perhaps in different ways, in the interaction of transferrin with reticulocytes, and that rabbit reticulocytes do not take up iron preferentially from one of the binding sites of bovine transferrin.
Collapse
|
36
|
Esparza I, Brock JH. The effect of trypsin digestion on the structure and iron-donating properties of transferrins from several species. BIOCHIMICA ET BIOPHYSICA ACTA 1980; 622:297-307. [PMID: 7378455 DOI: 10.1016/0005-2795(80)90040-9] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
The effect of trypsin digestion on iron-saturated and iron-free (apo) human, rabbit, bovine, pig and horse tranferrins has been studied. Iron-binding fragments were produced only from iron-saturated pig and bovine transferrins although some cleavage of the polypeptide chain occurred in all cases. The apo-transferrins were generally degraded to a greater extent than the corresponding iron-saturated proteins. The ability of the different transferrins to donate iron to rabbit reticulocytes varied in the order rabbit approximately pig greater than human approximately horse greater than bovine. Trypsin digestion considerably reduced the ability of pig and bovine transferrins to donate iron to rabbit reticulocytes, slightly reduced the iron-donating ability of rabbit transferrin, and had almost no effect on that of human or horse transferrins.
Collapse
|
37
|
Williams J, Moreton K. The distribution of iron between the metal-binding sites of transferrin human serum. Biochem J 1980; 185:483-8. [PMID: 7396826 PMCID: PMC1161376 DOI: 10.1042/bj1850483] [Citation(s) in RCA: 108] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The Makey & Seal [(1976) Biochim. Biophys. Acta 453, 250--256] method of polyacrylamide-gel electrophoresis in buffer containing 6 M-urea was used to determine the distribution of iron between the N-terminal and C-terminal iron-binding sites of transferrin in human serum. In fresh serum the two sites are unequally occupied; there is preferential occupation of the N-terminal site. On incubation of the serum at 37 degrees C the preference of iron for the N-terminal site becomes more marked. On storage of serum at -15 degrees C the iron distribution changes so that there is a marked preference for the C-terminal site. Dialysis of serum against buffer at pH 7.4 also causes iron to be bound much more strongly by the C-terminal than by the N-terminal site. The original preference for the N-terminal site can be resroted to the dialysed serum by addition of the diffusible fraction.
Collapse
|
38
|
Lineback-Zins J, Brew K. Preparation and characterization of an NH2-terminal fragment of human serum transferrin containing a single iron-binding site. J Biol Chem 1980. [DOI: 10.1016/s0021-9258(19)86237-3] [Citation(s) in RCA: 38] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
|
39
|
Strickland DK, Hudson BG. Structural studies on rabbit transferrin: isolation and characterization of the glycopeptides. Biochemistry 1978; 17:3411-8. [PMID: 687592 DOI: 10.1021/bi00609a035] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The structure of rabbit transferrin was investigated with regard to number, size, and composition of the heteropolysaccharide units and their relative location on the polypeptide chain. The composition and molecular weight of the Pronase glycopeptides revealed that rabbit transferrin contains two heteropolysaccharide units, each composed of 2 sialic acid residues, 2 galactose residues, 3 mannose residues, and 4-N-acetylglucosamine residues. The composition and molecular weight of the tryptic glycopeptides further substantiated the existence of two identical heteropolysaccharide units and revealed that both units have identical amino acid residues in the immediate vicinity of the carbohydrate attachment sites to the polypeptide chain, suggesting a sequence homology surrounding the two glycosylation sites. Characterization of the cyanogen bromide fragments from rabbit transferrin indicated that both heteropolysaccharide units are located within a single polypeptide fragment representing approximately one-third of the molecule.
Collapse
|
40
|
Evans RW, Williams J. Studies of the binding of different iron donors to human serum transferrin and isolation of iron-binding fragments from the N- and C-terminal regions of the protein. Biochem J 1978; 173:543-52. [PMID: 100104 PMCID: PMC1185808 DOI: 10.1042/bj1730543] [Citation(s) in RCA: 135] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
1. Trypsin digestion of human serum transferrin partially saturated with iron(III)-nitrilotriacetate at pH 5.5 or pH 8.5 produces a carbohydrate-containing iron-binding fragment of mol.wt. 43000. 2. When iron(III) citrate, FeCl3, iron (III) ascorabate and (NH4)2SO4,FeSO4 are used as iron donors to saturate the protein partially, at pH8.5, proteolytic digestion yields a fragment of mol.wt. 36000 that lacks carbohydrate. 3. The two fragments differ in their antigenic structures, amino acid compositions and peptide 'maps'. 4. The fragment with mol.wt. 36000 was assigned to the N-terminal region of the protein and the other to the C-terminal region. 5. The distribution of iron in human serum transferrin partially saturated with various iron donors was examined by electrophoresis in urea/polyacrylamide gels and the two possible monoferric forms were unequivocally identified. 6. The site designated A on human serum transferrin [Harris (1977) Biochemistry 16, 560--564] was assigned to the C-terminal region of the protein and the B site to the N-terminal region. 7. The distribution of iron on transferrin in human plasma was determined.
Collapse
|
41
|
Abstract
1. The distribution of iron between the two iron-binding sites in partially saturated ovotransferrin was studied by labelling with 55Fe and 59Fe and by gel electrophoresis in a urea-containing buffer. 2. When iron is added in the form of chelate complexes at alkaline pH, binding occurs preferentially at the N-terminal binding site. In acid, binding occurs preferentially at the C-terminal site. 3. When simple iron donors (ferric and ferrous salts) are used the metal is distributed at random between the binding sites, as judged by the gel-electrophoresis method. The double-isotope method shows a preference of ferrous salts for the N-terminal site. 4. Quantitative treatment of the results of double-isotope labelling suggests that in the binding of iron to ovotransferrin at alkaline pH co-operative interactions between the sites occur. These interactions are apparently absent in the displacement of copper and in the binding of iron at acid pH.
Collapse
|
42
|
Bluard-Deconinck JM, Williams J, Evans RW, van Snick J, Osinski PA, Masson PL. Iron-binding fragments from the N-terminal and C-terminal regions of human lactoferrin. Biochem J 1978; 171:321-7. [PMID: 656048 PMCID: PMC1183960 DOI: 10.1042/bj1710321] [Citation(s) in RCA: 36] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Digestion of lactoferrin with pepsin at pH3.0 gave an iron-binding half-molecule that represents the C-terminal part of the native protein. Tryptic or chymotryptic digestion of 30%-iron-saturated lactoferrin yielded the N- and C-terminal half molecules, which could be separated by DEAE-Sephadex chromatography. The N- and C-terminal fragments did not show any immunological cross-reaction. The carbohydrate of lactoferrin was distributed equally between the two fragments.
Collapse
|
43
|
Brock JH, Arzabe FR, Richardson NE, Deverson EV. Characterization of monoferric fragments obtained by tryptic cleavage of bovine transferrin. Biochem J 1978; 171:73-8. [PMID: 646825 PMCID: PMC1184134 DOI: 10.1042/bj1710073] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
1. The electrophoretically fast (F) and slow (S) fragments obtained by tryptic cleavage of bovine iron-saturated transferrin differed in carbohydrate content and peptide 'maps'. 2. A fragment capable of binding one Fe3+ ion per molecule was isolated after brief tryptic digestion of bovine apotransferrin and shown closely to resemble the S fragment obtained from the iron-saturated protein. 3. Fragments F and S are probably derived from the N- and C-terminal halves of the transferrin molecule respectively. 4. Bovine transferrin could donate iron to rabbit reticulocytes, but the monoferric fragments possessed little iron-donating ability.
Collapse
|
44
|
|
45
|
Evans RW, Donovan JW, Williams J. Calorimetric studies on the binding of iron and aluminium to the amino- and carboxyl-terminal fragments of hen ovotransferrin. FEBS Lett 1977; 83:19-22. [PMID: 562778 DOI: 10.1016/0014-5793(77)80632-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
|
46
|
|
47
|
|
48
|
Brock JH, Arzabe F, Lampreave F, Piñeiro A. The effect of trypsin on bovine transferrin and lactoferrin. BIOCHIMICA ET BIOPHYSICA ACTA 1976; 446:214-25. [PMID: 974113 DOI: 10.1016/0005-2795(76)90112-4] [Citation(s) in RCA: 80] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
The iron-saturated and iron-free (apo) forms of bovine transferrin and lactoferrin were digested with trypsin and the digests analysed by column chromatography and electrophoresis. Both of the iron-saturated proteins were more resistant to proteolysis than the corresponding apoproteins, and iron-transferrin was more resistant than iron-lactoferrin. Digestion of iron-transferrin yielded two iron-binding fragments with molecular weights of 32 000 and 38 500 whereas apotransferrin yielded only the larger fragment. In digests of lactoferrin, up to five different fragments with molecular weights ranging from 25 000 to 52 700 were detected, there being no obvious qualitative difference between digests of iron-lactoferrin and apolactoferrin. The susceptibility of apolactoferrin to tryptic digestion was only slightly reduced when apolactoferrin was complexed with beta-lactoglobulin, suggesting that complex-formation is not a mechanism for protecting lactoferrin against intestinal degradation. There was no immunological cross reaction between bovine transferrin or its digestion products against anti-lactoferrin antiserum, or vice-versa.
Collapse
|
49
|
Abstract
Two regions of the primary structure of human serum transferrin, of 87 and 57 residues, are reported. When these are suitably aligned by placing two gaps, 40 percent of the amino acids in corresponding positions are identical. This indicates that the doubling of an ancestral structural gene occurred during the evolution of the transferrins.
Collapse
|
50
|
Butterworth RM, Gibson JF, Williams J. Electron-paramagnetic-resonance spectroscopy of iron-binding fragments of hen ovotransferrins. Biochem J 1975; 149:559-63. [PMID: 173291 PMCID: PMC1165662 DOI: 10.1042/bj1490559] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
1. It is confirmed that there are two e.p.r. (electron-paramagnetic-resonance) signals associated with fully loaded ovotransferrin, which has two iron-binding sites. 2. Through experiments in which either of the two sites of whole ovotransferrin is occupied, the other being empty, the first occupied site is shown to belong to the N-terminal region of the protein; the second occupied site is in the C-terminal region. 3. When the protein is cleaved with trypsin or subtilisin, the N-terminal fragments are spectroscopically similar to the monoferric ovotransferrin complexes in which the iron atom occupies the N-terminal or C-terminal site respectively. Each fragment displays the same two e.p.r. signals, though not in the same proportions. 4. Computer summations of the e.p.r. spectra confirm that there is no iron-iron interaction which affects the spin Hamiltonian parameters at the iron-binding sites.
Collapse
|