Uteroferrin

Dobias B (1984) Surfactant Adsorption on Minerals Related to Flotation. 56 91-147 Doi K, Antanaitis BC, Aisen P (1988) The Binuclear Iron Centres of Uteroferrin and the Purple Acid Phosphatases. 70 1-26 Domcke W, see Bradshaw AM (1975) 24 133-170 Dophin D, see Morgan B (1987) 64 115-204... 

These considerations are the basis for the understanding of systems like porcine uteroferrin (19), acid phosphatases and methemerythrin (42), some of which will be discussed in this book. 

Figure 1. Characteristic EPR signals of Fe(II)Fe(III) sites in semimethemerythrinj (a), semimethemerythrinQ (b), reduced uteroferrin (c), reduced uteroferrin-molybdate complex (d), reduced bovine spleen purple acid phosphatase (e), reduced component A of methane monooxygenase (f). (Reproduced with permission from ref. 26. Copyright 1987 Elsevier.)...

Figure 3. First shell (1.1-2.3A) EXAFS spectra of methemerythrin azide, semimethemerythrin azide, ribonucleotide reductase B2 subunit, oxidized uteroferrin-phosphate complex, and reduced uteroferrin.

Figure 5. H-NMR spectrum of reduced (pink) and oxidized (purple) uteroferrin. (Reproduced with permission from ret 81. Copyright 1983 the authors.)...

Figure 6. Mossbauer spectra of the reduced uteroferrin phosphate complex at 55K (a) and 4.2K (b) and the oxidized uteroferrin-phosphate complex at 4.2K (c). (Reproduced with permission from ref. 90. Copyright 1986 American Society for Biological Chemists.)...

In the bovine case, the oxidation of the enzyme in the presence of phosphate is slow like that observed for uteroferrin (k = 0.07 min ) however, the color change and loss of EPR also follow kinetics similar to the loss of enzyme actvity. 

The magnetic interactions in the reduced porcine and bovine enzymes are considerably weaker than in the oxidized forms. The temperature dependences of the intensity of the EPR signals afford an estimate of -7 and -5.5 1 cm l for the J values of the reduced porcine and bovine enzymes, respectively (73,81). The large shifts observed in the NMR spectra of both enzymes also indicate that the coupling is weak from the temperature dependence of the isotropic shifts, J is estimated to be ca. -10 cm i for reduced uteroferrin (81). By analogy to the proposed structure for semimetHrNs, the reduced enzymes would have a hydroxo bridge. 

The half-life of Fe2(OH)2" at room temperature is a few seconds. An improved model for the kinetics of dissociation of this dinuclear cation recognizes significan articipation by Fe2(OH)3 + at higher pHs, thus clearing up earlier slight anomalies in this area. Phosphate ester hydrolysis at the di-iron center of uteroferrin has now been shown to involve nucleophilic attack by bridging hydroxide (as proposed but not conclusively demonstrated for several M—OH—M-containing catalytic species) rather than by hydroxide bonded to just one Fe. ... 

The emphasis on the study of hemoproteins and the iron-sulfur proteins often distracts attention from other iron proteins where the iron is bound directly by the protein. A number of these proteins involve dimeric iron centres in which there is a bridging oxo group. These are found in hemerythrin (Section 62.1.12.3.7), the ribonucleotide reductases, uteroferrin and purple acid phosphatase. Another feature is the existence of a number of proteins in which the iron is bound by tyrosine ligands, such as the catechol dioxygenases (Section 62.1.12.10.1), uteroferrin and purple acid phosphatase, while a tyrosine radical is involved in ribonucleotide reductase. The catecholate siderophores also involve phenolic ligands (Section 62.1.11). Other relevant examples are transferrin and ferritin (Section 62.1.11). These iron proteins also often involve carboxylate and phosphate ligands. These proteins will be discussed in this section except for those relevant to other sections, as noted above. 

In addition, a glycoprotein found in porcine uterine flushings contains iron and possesses acid phosphatase activity. This protein has been called uteroferrin, in view of its proposed role in the transport of iron from maternal to foetal circulation. On reduction, uteroferrin becomes pink in colour,... 

The bovine spleen enzyme is dimeric, has a molecular weight of nearly 40 000 and contains two iron centres.822 One of these can be removed reversibly by treatment of the protein with dithionite.823 Conflicting results have been reported for uteroferrin one group has found two iron atoms per 40 000 molecular weight,824 while another group reported one iron atom and molecular weight 35 000.825... 

Resonance Raman spectra of one-iron preparations of uteroferrin and the splenic acid phosphatase show that tyrosine is a ligand.826 The intense visible spectra of these proteins is due to tyrosine - Fem charge-transfer transitions. Two or three tyrosine residues are implicated. 

It has been shown8263 that the analysis of iron in uteroferrin is dependent on the presence of phosphate. Analysis of the native enzyme with one tightly bound phosphate gives an incorrect low answer suggesting the presence of only one iron. 

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. 

Figure 1. Comparison of the coordination spheres of the dinuclear iron sites in oxidized hemerythrin (Hr), ribonucleotide reductase (RNR), uteroferrin (Uf), and methane monooxygenase (MMO).

Purple acid phosphatases. Diiron-tyrosinate proteins with acid phosphatase activity occur in mammals, plants, and bacteria. Most are basic glycoproteins with an intense 510- to 550-nm light absorption band. Well-studied members come from beef spleen, from the uterine fluid of pregnant sows (uteroferrin), and from human macrophages and osteoclasts. " " One of the two iron atoms is usually in the Fe(III) oxidation state, but the second can be reduced to Fe(II) by mild reductants such as ascorbate. This half-reduced form is enzymatically active and has a pink color and a characteristic EPR signal. Treatment with oxidants such as H2O2 or hexacyannoferrate (III)... 

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