Carbamoylphosphat

Carbamoyl phosphate is the phosphorylated derivative of carbamic acid and a high-energy, reactive intermediate involved in both nitrogen metabolism and nucleotide biosynthesis. It is the mixed anhydride formed from carbamic acid and phosphoric acid and is typically produced inside cells by carbamoyl phosphate synthetases (CPS).

Two main enzymes generate carbamoyl phosphate in different cellular contexts. CPS I is a mitochondrial enzyme that drives the urea cycle in vertebrates, using ammonia (or ammonium derived from glutamine) and bicarbonate with ATP to form carbamoyl phosphate. CPS II is a cytosolic enzyme that participates in pyrimidine biosynthesis, using glutamine (as a nitrogen source) or ammonia with bicarbonate and ATP to produce carbamoyl phosphate.

The fate of carbamoyl phosphate depends on the biosynthetic route. In the urea cycle, it is transferred to ornithine by ornithine transcarbamylase to form citrulline, which proceeds toward urea production. In pyrimidine biosynthesis, carbamoyl phosphate reacts with aspartate via aspartate transcarbamoylase to form carbamoyl aspartate, a precursor to dihydroorotate and ultimately uridine monophosphate (UMP).

Chemically, carbamoyl phosphate is unstable in aqueous solution and is not generally isolated under physiological conditions. It is typically formed and consumed rapidly within enzyme complexes. Its role as a high-energy intermediate helps couple bicarbonate activation and nitrogen incorporation to downstream anabolic or catabolic pathways.

In summary, carbamoyl phosphate is a key phosphorylated carbamate intermediate produced by CPS I or CPS II, serving as the entry point for both the urea cycle and pyrimidine biosynthesis.