Pyrimidine metabolism

Pyrimidine biosynthesis occurs both in the body and through organic synthesis.

De novo biosynthesis of pyrimidine

carbamoyl phosphate synthetase II [1] carbamoyl phosphate This is the regulated step in the pyrimidine biosynthesis.
aspartic transcarbamolyase ( aspartate carbamoyl transferase) [1] carbamoyl aspartic acid -
dihhydroorotase [1] dihydroorotate Dehydration
dihydroorotate dehydrogenase [2] (the only mitochondrial enzyme) orotate Dihydroorotate then enters the mitochondria where it is oxidised through removal of hydrogens. This is the only mitochondrial step in nucleotide rings biosynthesis.
orotate phosphoribosyltransferase [3] OMP PRPP is used.
OMP decarboxylase [3] UMP Decarboxylation
uridine-cytidine kinase 2 [4] UDP Phosphorylation. ATP is used.
nucleoside diphosphate kinase UTP Phosphorylation. ATP is used.
CTP synthase CTP Glutamine and ATP are used.

The first three enzymes are all coded by the same gene in Metazoa ( CAD). In Fungi, a similar protein exists but lacks the dihydroorotase function: another protein catalyzes the second step.

In other organisms ( Bacteria, Archaea and the other Eukaryota), the first three steps are done by three different enzymes.

Other Languages
српски / srpski: Biosinteza pirimidina
srpskohrvatski / српскохрватски: Biosinteza pirimidina