Pyrimidine Metabolism in Rat Brain Cortex and Liver

Abstract

Pyrimidine nucleotide synthesis proceeds via a salvage pathway and a de novo pathway. In rat liver all enzymes involved in UMP syn­thesis from bicarbonate have a considerable activity (1–4), but in rat brain not all enzymes of the OA-pathway (orotic acid) have been demonstrated, although a significant incorporation of [¹⁴C]bicarbo­nate into OA was found (5). A considerable activity of uridine kinase is present in brain (6,7). OA and uracil can not pass the blood-brain barrier (8), but uridine can be taken up (9). In this study we com­pare the de novo and salvage pathways by measuring the incorporation of aspartate into OA and assaying the activities of DHOdehydrogenase (dihydroorotic acid dehydrogenase), OPRT (orotic acid phosphoribosyl­transferase), ODC (orotidylate decarboxylase), uridine kinase and uridine phosphorylase.