Uracil oxidase

Strains of Corynebacterium and Mycobacterium oxidized thymine and uracil to 5-methylbarbituric acid and barbituric acid, respectively, and it appeared that a single enzyme, uracil-thymine oxidase, was responsible for the oxidation of both bases (896) (Fig. 23). Uracil oxidase (398) and uracil-thymine oxidase (896) may be identical, since on purification of the former, the rates of oxidation of uracil and thymine remmned constant. A phosphorylated uracil-5-carbinol (2,4-dihydroxy-5-hydroxymethyl-pyrimidine) was isolated as an oxidation product of thymine by resting bacterial cells (398). However, the spectroscopic characteristics of the compound suggested that this compound may have been 5-methylbarbituric acid (896). 

Uracil derivatives can also function as herbicides by inhibition of the enzyme protoporphyrinogen-IX-oxidase (PRO), which is involved in the biosynthesis of chlorophyll <2006H(68)561>. Commercial examples of such PPO inhibitors include isocil 1104, bromacil 1105, terbacil 1106, flupropacil 1107, lenacil 1108, butafenacil 1109, and benzfendizone 1110 (Figure 9). 

Uracil (Ura, U) 199s, 203 tautomerism of 45 Urate oxidase 886 Urea 82s, 478s Urea carboxylase 730 Urease 478, 877,878... 

Aldehyde Oxidase. This enzyme is usually found in similar locations to xanthine oxidase or dehydrogenase and has been isolated from insects, birds, and mammals (20, 21). Aldehyde oxidase seems to be a poor choice of name for this enzyme because, while it oxidizes aldehydes to carboxylic acids, it also accepts a variety of purines and pyrimidines as oxidizable substrates. For example, aldehyde oxidase catalyzes the conversion of 2-hydroxypyrimidine to uracil and of adenine to 8-hydroxy-adenine (25). It appears that xanthine oxidase and aldehyde oxidase are... 

Caffeine (a trimethylxanthine ) is metabolized in the human liver by cytochrome P450 oxidase enzymes, which rip methyl groups off the caffeine molecule, producing three dimethylxanthines called paraxanthine (84%), theobromine (12%) and theophylline (4%) -followed by further demethylation and oxidation, leading to urates and uracil derivatives. 

From metabolic studies, an isotopic caffeine breath test has been developed that detects impaired liver function using the quantitative formation of labeled carbon dioxide as an index. From the urinary excretion of an acetylated uracil metabolite, human acet-ylator phenotype can be easily identified and the analysis of the ratio of the urinary concentrations of other metabolites represents a sensitive test to determine the hepatic enzymatic activities of xanthine oxidase and microsomal 3-methyl demethylation, 7-methyl demethylation, and 8-hydroxylation. Quantitative analyses of paraxanthine urinary metabolites may be used as a biomarker of caffeine intake. Fecal excretion is a minor elimination route, with recovery of only 2-5% of the ingested dose. 

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