ACPP and ACPT are members of the histidine acid phosphatase family which belongs to the histidine phosphatase superfamily that share a conserved catalytic core centred on a histidine. Mutation of an active site His-12 in ACPP abolished phosphatase activity (1). They have long been known to exhibit tyrosine phosphatase activity and dephosphorylate phosphotyrosine residues in proteins such as ErbB2 or ErbB4 (2).

Reference
1. Zhang XQ, Lee MS, Zelivianski S, Lin MF. (2001) Characterization of a prostate-specific tyrosine phosphatase by mutagenesis and expression in human prostate cancer cells. J Biol Chem, 276, 2544-50. PMID: 11067847
2. Fleisig H, El-Din El-Husseini A, Vincent SR. (2004) Regulation of ErbB4 phosphorylation and cleavage by a novel histidine acid phosphatase. Neuroscience, 127, 91-100. PMID: 15219672

    TULA/STS contains two members, UBASH3A/TULA-1 and UBASH3B/TULA-2. Sequence analysis shows that they share a conserved multidomain structure which contains an N-terminal ubiquitin-association domain, followed by a Src-homology 3 domain, and a C-terminal phosphatase domain. TULA/STS shows tyrosine phosphatase activity toward para-nitrophenyl phosphate, phosphotyrosine peptides and phosphoprotein ZAP70, Syk and certain Src family members. TULA/STS is distinct from other PTP which uses a cysteine residue as a catalytic residue (1). TULA/STS also belongs to the histidine phosphatase superfamily, that shares a conserved catalytic core centred on a histidine which is phosphorylated during the course of the reaction (2).

Reference
1. Chen, X., Ren, L., Kim, S., Carpino, N., Daniel, J.L., Kunapuli, S.P., Tsygankov, A.Y. and Pei, D. (2010) Determination of the substrate specificity of protein-tyrosine phosphatase TULA-2 and identification of Syk as a TULA-2 substrate. J Biol Chem, 285, 31268-31276. PMID: 20670933
2. Rigden DJ. (2008) The histidine phosphatase superfamily: structure and function. Biochem J, 409(2), 333-48. PMID: 18092946