Urea: obligate intermediate of pyrimidine-ring catabolism in Rhodosporidium toruloides

Abstract

Urea has been shown to be an obligate intermediate in and the penultimate product of the catabolism of pyrimidine-ring nitrogen in Rhodosporidium toruloides (Rhodotorula). One of a series of mutants selected for its inability to utilize uracil as a sole source of nitrogen was unable to utilize urea also. The mutant

Metabolism of dihydrouracil in Rhodosporidium toruloides

“…Although we did employ almost identical conditions of growth and enzyme assay, it is possible that the reductive pathway activity was masked by the oxidase activity seen in our strain. Even if catabolism in R. toruloides is initiated by a reduction of uracil to dihydrouracil, previous results (20) have shown that the penultimate step is similar to that of the oxidative pathway. Thus, ambiguity exists regarding pyrimidine-ring catabolism in R. toruloides.…”

“…Among these only the oxidative pathway, uracil -) barbituric acid --urea + malonic acid -* NH4 + C02, has been substantiated by independent investigations. This catabolic route seems to be limited to a few genera of procaryotes (8,9,11), yet labeled urea is produced from [2-14C]uracil or thymine in both mammalian and fungal systems (2,4,16,17,20). The mechanism for these conversions has not been established.…”

“…Media, growth tests, etc., used with R. toruloides have been described previously (20). Uracil was routinely used as a nitrogen source except as otherwise indicated.…”

“…Supplementation of whole cells with [2-14C]dihydrouracil, the determination of 14Co2 release, and the detection and identification of other radioactive products of metabolism have been described previously (20). Quantification of chromatogram radioactivity was determined with a Technical Associates radiochromatogram scanner.…”