Uracil degradation

Campbell LL (1957b) Rednctive degradation of pyrimidines II. Mechanism of uracil degradation by Clostridium uracilicum. J Bacteriol 73 225-229. 

COOH Oxaluric acid Fig. 24. Cerecedo s scheme for uracil degradation. ... 

Uracil degradation in mice is controlled by one allelic pair of the Pd locus. It was suggested that this locus regulates the activity of all three enzymes of the pyrimidine-degradation system dihydrouracil dehydrogenase, dihydropyrimidinase, and 3-ureidopropionase (Dagg et al., 1964). This was corroborated for 3-ureido-propionase by Sannaet al., 0970). 

Urea and uracil herbicides tend to be persistent in soils and may carry over from one season to the next (299). However, there is significant variation between compounds. Bromacil is debrominated under anaerobic conditions but does not undergo further transformation (423), linuron is degraded in a field soil and does not accumulate or cause carryover problems (424), and terbacd [5902-51-2] is slowly degraded in a Russian soil by microbial means (425). The half-hves for this breakdown range from 76 to 2,475 days and are affected by several factors including moisture and temperature. Finally, tebuthiuron apphed to rangeland has been shown to be phytotoxic after 615 days, and the estimated time for total dissipation of the herbicide is from 2.9 to 7.2 years (426). 

The final step in the metabolic degradation of uracil is the oxidation of malonic semialdehyde to give malonvl CoA. Propose a mechanism. 

The aerobic degradation of several azaarenes involves reduction of the rings at some stage, and are discussed in Chapter 10, Part 1. Illustrative examples include the degradation of pyridines (3-alkyl-pyridine, pyridoxal) and pyrimidines (catalyzed by dihydropyrimidine dehydrogenases). Reductions are involved in both the aerobic and the anaerobic degradation of uracil and orotic acid. 

Dihydropyrimidine dehydrogenase is the first and the rate-limiting enzyme in the three-step metabolic pathway involved in the degradation of the pyrimidine bases uracil and thymine. In addition, this catabolic pathway is the only route for the synthesis of p-alanine in mammals. 

CASRN 314-40-9 molecular formula C9Hi3BrN202 FW 261.12 Soil Metabolites tentatively identified in soil were 5-bromo-3-(3-hydroxy-l-methylpropyl)-6-methyluracil, 5-bromo-3-5ec-butyl-6-hydroxymethyluracil, 5-bromo-3-(2-hydroxy-l-methylprop-yl)-6-methyluracil, and carbon dioxide. The presence of uracil products suggests that bromacil was degraded via hydroxylation of the side chain alkyl groups. In the laboratory, 25.3% of C-bromacil degraded in soil to carbon dioxide after 9 wk but mineralization in the field was not observed. The half-life of bromacil in a silt loam was 5-6 months (Gardiner et al, 1969). 

In other studies it was found that 5-alkyluracils inhibited the degradation of uracil and thymine by rat tissue supernatants. It is believed that these compounds are competitors for dihydrouracil dehydrogenase, which catalyses the reduction of uracil and thymine [278]. 

The principles underlying the degradation of purines (1) and pyrimidines (2) differ. In the human organism, purines are degraded into uric acid and excreted in this form. The purine ring remains intact in this process. In contrast, the ring of the pyrimidine bases (uracil, thymine, and cytosine) is broken down into small fragments, which can be returned to the metabolism or excreted (for further details, see p. 419). 

These bases are then degraded to two P-amino acids, uracil to P-alanine and thymine to P-aminoisobutyrate. 

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