Carbamoyl phosphate synthetase I (CPS1 or CPSI) is a ligase enzyme located in the mitochondria involved in protein metabolism and the subsequent production of urea in animals. It transfers an ammonia molecule to a molecule of bicarbonate that has been phosphorylated by a molecule of ATP. The resulting carbamate is then phosphorylated with another molecule of ATP. The resulting molecule of carbamoyl phosphate leaves the enzyme. Abnormal or loss of the enzyme leads to CPS1 deficiency, a severe and deadly metabolic disorders.