Fig 2. Effect of the substrate and the inhibitor of allantoinase or dihydroorotase on the activity of dihydropyrimidinase using (A) 5-propyl-hydantoin or (B) dihydrouracil as a substrate.

Acetohydroxamate and 3-amino-1,2,4-triazole solutions, whose pH values, were pre-adjusted to pH 8. When using dihydrouracil as a substrate, some compounds at high concentrations were difficult to determine the inhibitory effect on the activity of dihydropyrimidinase using the spectrophotometric assay at 230 nm.