sentences:  The small subunit has a 3-layer beta/beta/alpha structure, and is thought to be mobile in most proteins that carry it.The C-terminal domain of the small subunit of CPSase has glutamine amidotransferase activity.The large subunit has two homologous carboxy phosphate domains, both of which have ATP-binding sites; however, the N-terminal carboxy phosphate domain catalyses the phosphorylation of biocarbonate, while the C-terminal domain catalyses the phosphorylation of the carbamate intermediate.