Pyrimidine catabolism

In parallel sequences of three reactions each, thymine is converted to beta-aminoisobutyrate and uracil is converted to beta-alanine. Both of these molecules are excreted in human urine and appear to be normal end products of pyrimidine catabolism. Mitochondrial AGXT2, however, can also catalyze the transamination of both molecules with pyruvate, yielding 2-oxoacids that can be metabolized further by reactions of branched-chain amino acid and short-chain fatty acid catabolism. The importance of these reactions in normal human pyrimidine catabolism has not been well worked out.

Summary from Reactome (R-HSA-73621), read 2026-09-23.