Pyrimidine metabolism features are all except

In Reye syndrome, cytosolic carbamoyl phosphate is increased as severely damaged mitochondria cannot utilize carbamoyl phosphate. Therefore, carbamoyl phosphate is diverted to the cytosol. It uses 2 multifunctional-multicatalytic polypeptides, which ensures efficient channeling of carbamoyl phosphate to pyrimidine synthesis. First 3 enzymes (i.e. CPS II, Aspartate transcarbamoylase and Dihydroorotase) are three different catalytic domain of single CAD polypeptide chain (a name derived from the 1st letter of each domain). Next (4th) non multifunctional enzyme DHOA dehydrogenase is the only mitochondrial enzyme. Orotate phosphoribosyltransferase and Orotidylate (OMP) decarboxylase are also catalytic domains of a single polypeptide chain of bifunctional enzyme UMP synthase. Orotic aciduria is caused by a defect of a single (type II) or both (type I) domains and results in poor growth, megaloblastic anemia and excretion of large amounts of orotate in urine. Uridine administration improves the condition. 6-Azauridine, following conversion to 6-azauridylate, competitively inhibits orotidylate decarboxylate and therefore causes orotic aciduria and orotidinuria.