THE METABOLISM OF URACIL

Oxygen uptake could not be demonstrated when uracil, uridine, or uridylic acid and various supplements were incubated with rat liver preparations. Attention was directed towards the likelihood that the initial step of uracil catabolism in mammals is a reduction such as occurs in yeasts. Various techniques were employed to measure the possible reduction of uracil to 4,5-dihydrouracil but no experimental evidence was uncovered that this latter compound was formed. While Canellakis has recently shown that the reaction uracil → 4,5-dihydrouracil does take place in mammalian tissues and that TRPH is required, this requirement must be specific since addition of DPNH in the experiments described below was without effect. A small fraction of the ureido carbon (C-2) of uracil-2-C 14 was released as carbon dioxide by rat liver slices. None of the results obtained can be reconciled with the oxidative pathway for uracil catabolism in mammals proposed by Cerecedo.