transcarbamoylase

Transcarbamoylase refers to a family of enzymes that transfer a carbamoyl group from a donor such as carbamoyl phosphate to an appropriate acceptor molecule. The two most well known members are ornithine transcarbamylase (OTC) and aspartate transcarbamoylase (ATCase), each serving distinct metabolic pathways.

Ornithine transcarbamylase catalyzes the condensation of ornithine with carbamoyl phosphate to produce citrulline and phosphate. This reaction is a key step in the urea cycle, which operates primarily in liver mitochondria to remove excess nitrogen by forming urea. Defects in OTC lead to OTC deficiency, an X-linked disorder characterized by hyperammonemia and, in some cases, elevated orotic acid levels due to diversion of carbamoyl phosphate into pyrimidine synthesis.

Aspartate transcarbamoylase catalyzes the first committed step in de novo pyrimidine biosynthesis by joining carbamoyl phosphate to aspartate, yielding carbamoyl aspartate and phosphate. ATCase is a classic allosteric enzyme whose activity is modulated by nucleotide effectors (for example, ATP stimulates while CTP inhibits in many organisms), thereby linking pyrimidine production to the cellular energetic state and nucleotide pool balance.

Beyond these examples, transcarbamoylases constitute a broader family of carbamoyltransferases found in bacteria, plants, and animals, where they participate in diverse cellular processes requiring carbamoyl transfer. Structural and regulatory features vary among family members, but their shared chemistry involves transfer of a carbamoyl group from a donor to an amine-containing substrate.