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Synthesis of Pyrimidine Ribonucleotides

This image is a scaled-down version of the actual pathway image. It does not contain any links to the protein information pages.


Synthesis of the Pyrimidines is less complex than that of the Purines, since the base is much simpler. Synthesis of Carbamoyl-P (Carbamoyl Phosphate) is the first reaction of Pyrimidine biosynthesis. Carbamoyl-P is formed from HCO3- (Bicarbonate) and the amide nitrogen of Glutamine by the cytosolic enzyme CPSase (Carbamoyl Phosphate Synthetase). This reaction consumes two molecules of ATP (Adenosine Monophosphate): One provides a phosphate group and the other energizes the reaction. Then condensation of Carbamoyl-P with Asp (Aspartate or L-Aspartate or Aspartic Acid) occurs to form CAA (N-Carbamoyl-L-Aspartate) which is catalyzed by ATCase (Aspartate Carbamoyltransferase). This reaction is the flux-generating step and occurs without need of ATP because Carbamoyl-P is intrinsically activated. The reaction forming Pyrimidine ring yields Dihydroorotate ((S)-4,5-Dihydroorotate) in [...]


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