Cytosolic CTP synthase 2 (CTPS) catalyzes the reaction of UTP, glutamine, ATP and water to form CTP, glutamate, ADP, and orthophosphate (Han et al. 2005; van Kuilenberg et al. 2000). Unpublished X-ray crystallographic data suggest that the enzyme is a tetramer (PDB 3IHL). Both CTPS2 and a second human gene product, CPTS, have CTP synthase activity in various test systems; their relative contributions to CTP metabolism in the body is not clear.