Uterine purple phosphatase

A phosphoprotein phosphatase from beef spleen contains one atom of iron per molecule (Campbell and Zerner, 1973) and is activated by reducing agents. Similar iron-containing phosphatases have been isolated from Neurospora crassa (Jacobs et al, 1971) and kidney beans (Nochmunson et al, 1974). 

Vanngird, T., and Dunford, H. B., 1975, Biochim. Biophys. Acta 391 259. 

Abragam, A., and Bleaney, B., 1970, Electron Paramagnetic Resonance of Transition Ions, Oxford University Press, England. 

in The Structure and Function of Oxidation-Reduction Enzymes, Wenner-Gren Symposia, p. 327, Pergamon Press, Stockholm. 

Antonini, E., and Brunori, M., 1971, Hemoglobin and Myoglobin and Their Reactions with Ligands, North-Holland Publishing Co., Amsterdam. 

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PAPs are glycoenzymes of 35-40kDa characterized by their intense purple color due to a tyrosine ligand-to-iron(III) charge transfer transition near 600 nm. The best studied PAPs are those from bovine spleen, porcine uterine fluids, and rat bone, which have been proposed to be involved in iron transport, the immune response, and bone resorption respectively. However, the biological relevance of the phosphatase activity of PAPs has not been unequivocally established. Recently, a bacterial phospholipase with active site properties resembling those of PAPs has also been reported. All PAPs contain a conserved dimetal binding... 

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)... 

Add phosphatases are ubiquitously distributed enzymes defined by the pH optimum (usually 4.9-6.0) of their hydrolytic activity toward orthophosphate monoesters. A metal-dependent subclass of these enzymes was first recognized in 1973, when iron-bearing acid phosphatases were isolated from porcine uterine fluid and bovine spleen Because of their intense colors they have become known as the purple add phosphatases. Its source, content of iron, and presumed role in iron transport fix>m pregnant sow to fetal pig have earned the pordne protein the euphonious name of uteroferrin. 

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. 

Unlike uteroferrin, which produces a single band of expected mobility for its molecular size by SDS-FAGE, bovine spleen add phosphatase yields two bands, even when isolated in the continuous presence of proteolytic inhibitors However, the extensive sequence homology between the spleen and uterine enzyme, and the fact that isolation of the spleen enzyme is accomplished by prolonged add extraction of spleen homogenates, make it likely that the purple add phosphatase of spleen is also a single-chain protein ... 

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