Rapid conversion of newly-synthesized orotate to uridine-5-monophosphate by rat liver cytosolic enzymes.

It had been noted previously that the activity of mitochondrial dihydroorotate dehydrogenase was lower in crude tissue preparations containing cytosol than in isolated mitochondria. Closer examination reveals that the apparent lower enzyme activity is due to rapid conversion of newly-synthesized orotate to uridine-5-monophosphate by the cytosolic enzymes, orotate phosphoribosyltransferase and orotidylate decarboxylase.