Cloning, expression, and characterization of a human inosine triphosphate pyrophosphatase encoded by the ITPA gene

ITP and dITP exist in all cells. dITP is potentially mutagenic, and the lev els of these nucleotides are controlled by inosine triphosphate pyrophospha tase (EC 3,6,1,19), Here we report the cloning, expression, and characteriz ation of a 21,5-kDa human inosine triphosphate pyrophosphatase (hITPase), a n enzyme whose activity has been reported in many animal tissues and studie d in populations but whose protein sequence has not been determined before. At the optimal pH of 10.0, recombinant hITPase hydrolyzed ITP, dITP, and x anthosine 5'-triphosphate to their respective monophosphates whereas activi ty with other nucleoside triphosphates was low. K-m values for ITP, dITP, a nd xanthosine 5'-triphosphate were 0,51, 0,31, and 0.57 mM, respectively, a nd k(cat) values were 580, 360, and 640 s(-1) respectively. A divalent cati on was absolutely required for activity. The gene encoding the hITPase cDNA sequence was localized by radiation hybrid mapping to chromosome 20p in th e interval D20S113-D20S97, the same interval in which the ITPA inosine trip hosphatase gene was previously localized. A BLAST search revealed the exist ence of many similar sequences in organisms ranging from bacteria to mammal s. The function of this ubiquitous protein family is proposed to be the eli mination of minor potentially mutagenic or clastogenic purine nucleoside tr iphosphates from the cell.