Carbamoyl phosphate synthetase I (CPS I)
Cofactors used
Clinical / pharmacological. CPS I deficiency: hyperammonaemia, normal orotic acid
What it does, reaction by reaction
Urea Cycle Amino Acid & Nitrogen Metabolism · Mitochondrial matrix + cytosol
NH₄⁺ + HCO₃⁻ + 2 ATP → carbamoyl phosphate + 2 ADP + Pᵢ
Converts NH4+ HCO3- ATP into Carbamoyl phosphate ADP Pi
› Notes
In the mitochondrial matrix, carbamoyl phosphate synthetase I (CPS I) uses MgATP and requires N-acetylglutamate (NAG) as an obligatory allosteric activator. This is the rate-limiting, committed, and essentially irreversible step of the urea cycle; it consumes two high-energy phosphate bonds.
Showing all 1 reactions.
What accelerates and inhibits it
Regulation is pathway-specific, so each context is listed separately
Urea Cycle
N-acetylglutamate (obligatory); increased mitochondrial ammonia
Absence of N-acetylglutamate; no principal direct physiologic inhibitor
Glucagon and cortisol increase expression during fasting/high-protein catabolism; insulin lowers net ureagenic demand in the fed state
Recent literature
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