BIOSYNTHESIS OF NUCLEOTIDES IN WHEAT: IV. METABOLISM OF SPECIFICALLY14C-LABELED OROTIC ACID

The biosynthesis of pyrimidine nucleotides in wheat leaves was investigated, with specifically14C-labeled orotic acids as precursors. The utilization of orotic acid, unlike uracil, for the synthesis of pyrimidine nucleotides is far more predominant than the degradative process. The labeled orotic acid was rapidly metabolized to uracil nucleotides and the sugar nucleotide, uridine-5′-diphosphate glucose. However, cytosine nucleotides were not significantly labeled within 60 minutes. In spite of the fact that no detectable radioactive OMP was observed, the results presented indicate strongly that the biosynthetic pathway for pyrimidine nucleotides from orotic acid in this plant proceeds according to the following reactions: orotic acid + 5-phosphoribosyl-1-pyrophosphate → orotidine-5′-monophosphate → uridine-5′-monophosphate → uridine-5′-triphosphate → uridine-5′-diphosphate glucose, and uridine-5′-triphosphate → cytidine-5′-triphosphate.