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carbamoyl-phosphate synthase, large subunit Carbamoyl-phosphate synthase (CPSase) catalyzes the first committed step in pyrimidine, arginine, and urea biosynthesis. In general, it is a glutamine-dependent enzyme, EC 6.3.5.5, termed CPSase II in eukaryotes. An exception is the mammalian mitochondrial urea-cycle form, CPSase I, in which the glutamine amidotransferase domain active site Cys on the small subunit has been lost, and the enzyme is ammonia-dependent. In both CPSase I and the closely related, glutamine-dependent CPSase III (allosterically activated by acetyl-glutamate) demonstrated in some other vertebrates, the small and large chain regions are fused in a single polypeptide chain. This model represents the large chain of glutamine-hydrolysing carbamoyl-phosphate synthases, or the corresponding regions of larger, multifunctional proteins, as found in all domains of life, and CPSase I forms are considered exceptions within the family. In several thermophilic species (Methanobacterium thermoautotrophicum, Methanococcus jannaschii, Aquifex aeolicus), the large subunit appears split, at different points, into two separate genes. [Purines, pyrimidines, nucleosides, and nucleotides, Pyrimidine ribonucleotide biosynthesis] |
Jiyao W et al.(2023). "The conserved domain database in 2023.",