Abstract
In humans, the pathway for the catabolism of uracil and thymine consists of three consecutive steps. Dihydropyrimidine dehydrogenase catalyzes the reduction of uracil and thymine to 5,6-dihydrouracil and 5,6-dihydrothymine, respectively. The second step is catalyzed by dihydropyrimidinase and consists of reversible hydrolysis of 5,6-dihydrouracil and 5,6-dihydrothymine to N -carbamyl-β-alanine and N -carbamyl-β-aminoisobutyric acid, respectively. Finally, β-ureidopropionase catalyzes the conversion of N -carbamyl-β-alanine and N -carbamyl-β-aminoisobutyric acid to β-alanine and β-aminoisobutyric acid, respectively, ammonia, and CO2. Patients with a defect in one of the enzymes of the pyrimidine degradation pathway can be diagnosed by an aberrant excretion profile of the pyrimidine bases and their degradation products in urine (1). For example, in patients with a complete deficiency of dihydropyrimidinase, highly increased concentrations of 5,6-dihydrouracil and 5,6-dihydrothymine and moderately increased concentrations of uracil and thymine can be detected in urine. It has also …
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