Pyrophosphatase that hydrolyzes the non-canonical purine nucleotides inosine triphosphate (ITP), deoxyinosine triphosphate (dITP) as well as 2'-deoxy-N-6-hydroxylaminopurine triphosphate (dHAPTP) and xanthosine 5'-triphosphate (XTP) to their respective monophosphate derivatives. The enzyme does not distinguish between the deoxy- and ribose forms. Probably excludes non-canonical purines from RNA and DNA precursor pools, thus preventing their incorporation into RNA and DNA and avoiding chromosomal lesions. a ribonucleoside 5'-triphosphate + H2O = a ribonucleoside 5'-phosphate + diphosphate + H(+) a 2'-deoxyribonucleoside 5'-triphosphate + H2O = a 2'-deoxyribonucleoside 5'-phosphate + diphosphate + H(+) H2O + ITP = diphosphate + H(+) + IMP dITP + H2O = dIMP + diphosphate + H(+) H2O + XTP = diphosphate + H(+) + XMP Binds 1 Mg(2+) ion per subunit. kcat is 580 sec(-1) with ITP as substrate (PubMed:11278832). kcat is 360 sec(-1) with dITP as substrate (PubMed:11278832). kcat is 640 sec(-1) with XTP as substrate (PubMed:11278832). kcat is 79.6 sec(-1) with dITP as substrate (PubMed:17090528). kcat is 85.3 sec(-1) with dHAPTP as substrate (PubMed:17090528). kcat is 12.1 sec(-1) with dGTP as substrate (PubMed:17090528). Optimum pH is 10. Homodimer. Ubiquitous. Highly expressed in heart, liver, sex glands, thyroid and adrenal gland. The disease is caused by variants affecting the gene represented in this entry. Three different human populations have been reported with respect to their ITPase activity: high, mean (25% of high) and low activity. The variant Thr-32 is associated with complete loss of enzyme activity, may be by altering the local secondary structure of the protein. Heterozygotes for this polymorphism have 22.5% of the control activity: this is consistent with a dimeric structure of the enzyme. The disease is caused by variants affecting the gene represented in this entry. Belongs to the HAM1 NTPase family.