Phosphatase that hydrolyzes non-canonical purine nucleotides such as XTP and ITP to their respective diphosphate derivatives. Probably excludes non-canonical purines from DNA/RNA precursor pool, thus preventing their incorporation into DNA/RNA and avoiding chromosomal lesions. ITP and XTP are the best substrates, followed by GDP and dITP. Is not active on dATP and dGTP, and exhibits no phosphatase activity toward pyrimidines (CTP, TTP, UTP, dCTP, and dTTP) (PubMed:16216582). Seems also implicated in the resistance against the thiamine metabolism inhibitors bacimethrin and CF3-HMP (PubMed:15292217). H2O + XTP = H(+) + phosphate + XDP H2O + ITP = H(+) + IDP + phosphate Binds 1 divalent cation per subunit. Activity is maximal in the presence of Mg(2+), while Mn(2+) decreases the activity by 20%. Competitively inhibited by ATP, GTP and TTP. kcat is 573.3 sec(-1) with ITP as substrate. kcat is 2625 sec(-1) with XTP as substrate. kcat is 119 sec(-1) with GDP as substrate. kcat is 616.5 sec(-1) with dITP as substrate. kcat is 22.3 sec(-1) with GTP as substrate. Optimum pH is 6.75. Homodimer. Belongs to the YjjX NTPase family. PubMed:7841459 sequence was originally thought to originate from S.typhimurium, but seems to come from an unknown E.coli strain. Extended N-terminus.