Pyrophosphatase that catalyzes the hydrolysis of nucleoside triphosphates to their monophosphate derivatives, with a high preference for the non-canonical purine nucleotides XTP (xanthosine triphosphate), dITP (deoxyinosine triphosphate) and ITP (PubMed:12297000, PubMed:17976651). Can also efficiently hydrolyze 2'-deoxy-N-6-hydroxylaminopurine triphosphate (dHAPTP) (PubMed:17090528). Seems to function as a house-cleaning enzyme that removes non-canonical purine nucleotides from the nucleotide pool, thus preventing their incorporation into DNA/RNA and avoiding chromosomal lesions (PubMed:12297000, PubMed:12730170, PubMed:17090528). To a much lesser extent, is also able to hydrolyze GTP, dGTP and dUTP, but shows very low activity toward the canonical nucleotides dATP, dCTP and dTTP and toward 8-oxo-dGTP, purine deoxyribose triphosphate, 2-aminopurine deoxyribose triphosphate and 2,6-diaminopurine deoxyribose triphosphate (PubMed:12297000, PubMed:17090528). H2O + XTP = diphosphate + H(+) + XMP dITP + H2O = dIMP + diphosphate + H(+) H2O + ITP = diphosphate + H(+) + IMP Binds 1 divalent metal cation per subunit. Maximum activity is obtained with Mg(2+). Activity with Mn(2+) or Ni(2+) makes up 60-75% of the maximum rate. Vmax values are similar for XTP, dITP and ITP. Activity toward dATP, dCTP and dTTP is less than 1% of the rate of XTP hydrolysis. dGTP and dUTP are hydrolyzed at 10-12% of the rate of XTP hydrolysis (PubMed:12297000). kcat is 5.7 sec(-1) with ITP or dHAPTP as substrate. kcat is 1.5 sec(-1) with dGTP as substrate (at pH 9.5 and 37 degrees Celsius) (PubMed:17090528). kcat is 19.9 sec(-1) with XTP as substrate. kcat is 13.2 sec(-1) with dITP as substrate. kcat is 18.9 sec(-1) with ITP as substrate. kcat is 0.85 sec(-1) with GTP as substrate. kcat is 0.37 sec(-1) with dGTP as substrate. kcat is 0.26 sec(-1) with TTP as substrate (at pH 9.0 and 37 degrees Celsius) (PubMed:17976651). Optimum pH is 10-10.5 (PubMed:12297000). Optimum pH is 9.0 (PubMed:17976651). Reaction rates under neutral conditions are <40% of the maximum (PubMed:12297000). Homodimer. Inactivation of this gene in a moa background (cells deficient in molybdopterin biosynthesis) results in increased N-6-hydroxylaminopurine (HAP) sensitivity, an increase in the level of mutagenesis, and increased recombination and SOS induction upon HAP exposure. Modified or damaged nucleotides such as 6-chloropurine deoxyribose triphosphate, 8-Br-dGTP, 5-Br-dCTP, 5-Br-dUTP, 7-deaza-dGTP, 7-methyl-GTP, N6-etheno-ATP, NAD, NADH, FAD, ADP-ribose, UPD-glucose, AppA and ApppA are not hydrolyzed by the enzyme. The aberrant nucleotides XTP and dITP can be produced by oxidative deamination from purine nucleotides in cells; they are potentially mutagenic. Belongs to the HAM1 NTPase family.