This entry represents the type 1 glutamine amidotransferase (GATase1) domain found in Cytidine Triphosphate Synthetase (CTP). CTP is involved in pyrimidine ribonucleotide/ribonucleoside metabolism. CTPs produce CTP from UTP and glutamine and regulate intracellular CTP levels through interactions with four ribonucleotide triphosphates. The enzyme exists as a dimer of identical chains that aggregates as a tetramer [].CTP is derived form UTP in three separate steps involving two active sites. In one active site, the UTP O4 oxygen is activated by Mg-ATP-dependent phosphorylation, followed by displacement of the resulting 4-phosphate moiety by ammonia. At a separate site, ammonia is generated via rate limiting glutamine hydrolysis (glutaminase) activity []. A gated channel that spans between the glutamine hydrolysis and amidoligase active sites provides a path for ammonia diffusion. CTPs belong to the triad family of amidotransferases having a conserved Cys-His-Glu catalytic triad in the glutaminase active site [].
