InterPro domain: IPR008963

Purple acid phosphatases (PAPs) are ubiquitous binuclear metal-containing acid hydrolases characterised by their acidic pH optima and their intense purple colour due to a TyrO-to-FeIII charge-transfer transition. The amino acid residues coordinating the metal ions are conserved in all PAPs. Active PAPs contain an FeIII ion coordinated to Tyr O, a His N, and an Asp O ₂ , in addition to a divalent metal ion (Fe, Zn, or Mn) coordinated by a His N, a His N, and an Asn O. A hydroxide ion and an Asp O ₂ bridge the two metal ions [ 1 ]. These enzymes share a high degree of homology within their N-termini [ 2 ].

This entry also includes phospholipase D, the structure of which has been solved from Bacillus subtilis and shows a purple acid phosphatase-like fold [ 3 ].

1. New insights into the mechanism of purple acid phosphatase through (1)H NMR spectroscopy of the recombinant human enzyme. J. Am. Chem. Soc. 124, 13974-5
2. Binuclear metal centers in plant purple acid phosphatases: Fe-Mn in sweet potato and Fe-Zn in soybean. Arch. Biochem. Biophys. 370, 183-9
3. Crystal structure of the Bacillus subtilis phosphodiesterase PhoD reveals an iron and calcium-containing active site. J. Biol. Chem. 289, 30889-99