Purple acid phosphatases

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Purple acid phosphatases (PAPs) (EC are metalloenzymes that hydrolyse phosphate esters and anhydrides under acidic condition.[1][2] In their oxidised form, PAPs in solution are purple in colour. This is due to the presence of a dinuclear iron centre,[3] to which a tyrosine residue is connected via a charge transfer.[4] This metallic centre is composed of Fe3+ and M, where M is Fe3+, Zn2+, Mg2+ or Mn2+. The conserved Fe3+ is stabilised in the ferric form, whereas M may undergo reduction. Upon treatment with mild reductants, PAPs are converted to their enzymatically active, pink form. Treatment with strong reducing agents dissociates the metallic ions, and renders the enzyme colourless and inactive.[5]

PAPs are highly conserved within eukaryotic species, with >80% amino acid homology in mammalian PAPs,[6] and >70% sequence homology in PAPs of plant origin.[7] However sequence analysis reveals that there is minimal homology between plant and mammal PAPs (<20%), except for the metal-ligating amino acid residues which are identical.[8] The metallic nucleus of PAPs also varies between plants and mammals. Mammalian PAPs which have been isolated and purified have, to this point, been composed exclusively of iron ions, whereas in plants the metallic nucleus is composed of Fe3+ and either Zn2+ or Mn2+. PAPs have also been isolated in fungi, and DNA sequences encoding for possible PAPs have been identified in prokaryotic organisms, such as in Cyanobacteria spp. and Mycobacteria spp.[9]

Currently there is no defined nomenclature for this group of enzymes, and a variety of names exists. These include purple acid phosphatase (PAP), uteroferrin (Uf), type 5 acid phosphatase (Acp 5) and tartrate resistant acid phosphatase (TRAP, TRACP, TR-AP). There is, however, a consensus in the literature that purple acid phosphatase (PAP) relates to those found in non-mammalian species and tartrate resistant acid phosphatase (TRAP) to those found in mammalian species.

Uteroferrin, bovine spleen PAP and tartrate resistant acid phosphatase all refer to mammalian PAPs, whereby research on PAPs expressed in various tissues diverged. Subsequent research has proven that all of these enzymes are the same entity.[10][11]


  1. ^ B. C. Antanaitis; P. Aisen (1983). "Uteroferrin and the purple acid phosphatases". Advances in Inorganic Biochemistry. 5: 111–136. PMID 6382957.
  2. ^ David C. Schlosnagle; Fuller W. Bazer; John C. M. Tsibris; R. Michael Roberts (December 1974). "An iron-containing phosphatase induced by progesterone in the uterine fluids of pigs". Journal of Biological Chemistry. 249 (23): 7574–9. PMID 4373472.
  3. ^ Antanaitis BC, Aisen P (February 1984). "Stoichiometry of iron binding by uteroferrin and its relationship to phosphate content". Journal of Biological Chemistry. 259 (4): 2066–2069. PMID 6698956.
  4. ^ Bruce P. Gaber; James P. Sheridan; Fuller W. Bazer; R. Michael Roberts (September 1979). "Resonance Raman scattering from uteroferrin, the purple glycoprotein of the porcine uterus". Journal of Biological Chemistry. 254 (17): 8340–8342. PMID 468828.
  5. ^ Jussi M. Halleen; Helena Kaija; Jan J. Stepan; Pirkko Vihko; H. Kalervo Väänänen (April 1998). "Studies on the protein tyrosine phosphatase activity of tartrate-resistant acid phosphatase". Archives of Biochemistry and Biophysics. 352 (1): 97–102. doi:10.1006/abbi.1998.0600. PMID 9521821.
  6. ^ Deirdre K. Lord; Nicholas C. P. Cross; Maria A. Bevilacqua; Susan H. Rider; Patricia A. Gorman; Ann V. Groves; Donald W. Moss; Denise Sheer; Timothy M. Cox (April 1990). "Type 5 acid phosphatase. Sequence, expression and chromosomal localization of a differentiation-associated protein of the human macrophage". European Journal of Biochemistry. 189 (2): 287–293. doi:10.1111/j.1432-1033.1990.tb15488.x. PMID 2338077.
  7. ^ Gerhard Schenk; Yubin Ge; Lyle E. Carrington; Ceridwen J. Wynne; Iain R. Searle; Bernard J. Carroll; Susan Hamilton; John de Jersey (October 1999). "Binuclear metal centers in plant purple acid phosphatases: Fe-Mn in sweet potato and Fe-Zn in soybean". Archives of Biochemistry and Biophysics. 370 (2): 183–189. doi:10.1006/abbi.1999.1407. PMID 10510276.
  8. ^ Thomas Klabunde; Norbert Sträter; Bernt Krebs; Herbert Witzel (June 1995). "Structural relationship between the mammalian Fe(III)-Fe(II) and the Fe(III)-Zn(II) plant purple acid phosphatases". FEBS Letters. 367 (1): 56–60. doi:10.1016/0014-5793(95)00536-I. PMID 7601285.
  9. ^ Gerhard Schenk; Michael L. J. Korsinczky; David A. Hume; Susan Hamilton; John DeJersey (September 2000). "Purple acid phosphatases from bacteria: similarities to mammalian and plant enzymes". Gene. 255 (2): 419–424. doi:10.1016/S0378-1119(00)00305-X. PMID 11024303.
  10. ^ Barbro Ek-Rylander; Per Bill; Maria Norgård; Stefan Nilsson; Göran Andersson (December 1991). "Cloning, sequence, and developmental expression of a type 5, tartrate-resistant, acid phosphatase of rat bone". Journal of Biological Chemistry. 266 (36): 24684–24689. PMID 1722212.
  11. ^ Ping Ling; R. Michael Roberts (April 1993). "Uteroferrin and intracellular tartrate-resistant acid phosphatases are the products of the same gene". Journal of Biological Chemistry. 268 (10): 6896–6902. PMID 8463220.

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