The pyrimidine ring, unlike the purine ring, is degraded in humans and forms highly soluble products such as β-alanine and β-aminoisobutyrate. This degradation process generates ammonia and CO2. Pyrimidine bases can be recycled into nucleosides, which can then be phosphorylated into nucleotides. However, due to their high solubility, the clinical significance of pyrimidine salvage is not as significant as purine salvage. It is worth noting that the salvage of pyrimidine nucleosides is the basis for using uridine in the treatment of hereditary orotic aciduria.
Unlike the purine ring, which is not cleaved in humans and is excreted as poorly soluble uric acid, the pyrimidine ring is opened and degraded to highly soluble products, β-alanine (from the degradation of CMP and UMP) and β-aminoisobutyrate (from TMP degradation), with the production of ammonia and CO2. Pyrimidine bases can be salvaged to nucleosides, which are phosphorylated to nucleotides. However, their high solubility makes pyrimidine salvage less significant clinically than purine salvage. [Note: The salvage of pyrimidine nucleosides is the basis for using uridine in the treatment of hereditary orotic aciduria (see p. 302).]
VII. CHAPTER SUMMARY