This entry includes purple acid phosphatases (EC 3.1.3.2), which are metal dependent, binding two metal ions. Metal binding ligands and residues involved in resistance to tartrate inhibition are conserved [].Purple acid phosphatase 3, 4, 7, 8 and 17 are found in plants, bind zinc and iron, and the genes are predominantly transcribed in flowers []. Purple acid phosphatase 17 (PAP17) is induced in response to phosphate starvation, a condition occurring in phosphate-poor soils, and the plant hormone abscisic acid (ABA) and salt stress. Like mammalian acid phosphatase 5, PAP17 has peroxidation activity [].Acid phosphatase 5 (ACP5; EC 3.1.3.2) removes the mannose 6-phosphate recognition marker from lysosomal proteins. The exact site of dephosphorylation is not clear. Evidence suggests dephosphorylation may take place in a prelysosomal compartment as well as in the lysosome []. ACP5 belongs to the metallophosphatase (MPP) superfamily. MPPs are functionally diverse, but all share a conserved domain with an active site consisting of two metal ions (usually manganese, iron, or zinc) co-ordinated with octahedral geometry by a cage of histidine, aspartate, and asparagine residues [].
