Purple acid phosphatases Uteroferrin

Bernhardt PV, Schenk G, Wilson GJ. 2004. Direct electrochemistry of porcine purple acid phosphatase (uteroferrin). Biochemistry 43 10387-10392. 

Twitchett MB, Schenk G, Aquino MAS, Yiu DTY, Lau TC, Sykes AG. 2002. Reactivity of M metal-substituted derivatives of pig purple acid phosphatase (Uteroferrin) with phosphate. Inorg Chem 41 5787-5794. 

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... 

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.)...

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. 

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. 

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)... 

The presentation in 1993 of the structure of the hydroxylase component of methane monooxygenase (MMOH) by Rosenzweig et al. (15) is the third published three-dimensional structure of a diiron-oxygen protein (Fig. 1). The previous two are from hemerythrin (Hr) (16,17) and protein R2 of E. coli ribonucleotide reductase (RNR-R2) (18, 19). Some other dinuclear iron proteins with known fi-oxo or p.-hydroxo bridges are purple acid phosphatases (PAP) [(e.g., uteroferrin (Uf)] (20, 21), ferritins (in early stages of nucleation) (22), rubrerythrin (Rr) (23-26), nigerythrin (26), and soluble stearoyl-acyl carrier protein A desaturase (A-AGP) (27, 28). 

The purple acid phosphatases (PAP) catalyze the hydrolysis of phosphate esters under acidic pH conditions (pH optimum 5) (9, 10). They differ from other acid phosphatases in having a distinct purple color due to the presence of iron or manganese and in being uninhibited by tartrate. Diiron units have been found in the active sites of the enzymes from mammalian spleen (171-173) and uterus (173, 174), while a heterodinu-clear FeZn unit has been characterized for the enzyme from red kidney bean (175). Either the Fe2 or the FeZn unit is catalytically competent in these enzymes, since the enzymes from porcine uterus and bovine spleen can be converted into active FeZn forms and the kidney bean enzyme can be transformed into an active Fe2 form (176). There are also enzymes from other plant sources (particularly sweet potato) that have been reported to have either a mononuclear Mn(III) or Fe(III) active site (177), but these are beyond the scope of the review. This section will focus on the enzymes from porcine uterus (also called uteroferrin), bovine spleen, and red kidney bean. 

The Binuclear Iron Centers of Uteroferrin and the Purple Acid Phosphatases ... 

In addition to its archetypical members, uteroferrin and bovine spleen add phosphatase, the class of purple add phosphatases includes proteins isolated from rat bone and. spleen spleens of patients with Gaucher s disease or leukemic reticuloen-dotheliosis equine uterine flushings bovine cortical bone giant ceU tumors human placenta and microorganisms . The plant enzymes include an Fe-Zn phosphatase from red kidney beans and an Fe-Fe or Mn(in) protein from sweet potato tubers . Although less well-defined and more heterogeneous than their mammalian counterparts, the color and iron content of the plant enzymes warrant their designation as purple acid phosphatases. 

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