thiouracil and pyrimidine

The pathogenic protozoan parasite Leishmania donovani is capable of both de novo pyrimidine biosynthesis and salvage of pyrimidines from the host milieu. Genetic analysis has authenticated L. donovani uracil phosphoribosyltransferase (LdUPRT), an enzyme not found in mammalian cells, as the focal enzyme of pyrimidine salvage because all exogenous pyrimidines that can satisfy the requirement of the parasite for pyrimidine nucleotides are funneled to uracil and then phosphoribosylated to UMP in the parasite by LdUPRT. To characterize this unique parasite enzyme, LdUPRT was expressed in Escherichia coli, and the recombinant enzyme was purified to homogeneity. Kinetic analysis revealed apparent Km values of 20 and 99 μM for the natural substrates uracil and phosphoribosylpyrophosphate, respectively, as well as apparent Km values 6 and 7 μM for the pyrimidine analogs 5-fluorouracil and 4-thiouracil, respectively. Size exclusion chromatography revealed the native LdUPRT to be tetrameric and retained partial structure and activity in high concentrations of urea. L. donovani mutants deficient in de novo pyrimidine biosynthesis, which require functional LdUPRT for growth, are hypersensitive to high concentrations of uracil, 5-fluorouracil, and 4-thiouracil in the growth medium. This hypersensitivity can be explained by the observation that LdUPRT is substrate-inhibited by uracil and 4-thiouracil, but 5-fluorouracil toxicity transpires via an alternative mechanism. This substrate inhibition of LdUPRT provides a protective mechanism for the parasite by facilitating purine and pyrimidine nucleotide pool balance and by sparing phosphoribosylpyrophosphate for consumption by the nutritionally indispensable purine salvage process.

Topics: Cations, Divalent; Chromatography, Gel; Enzyme Stability; Feedback, Physiological; Fluorouracil; Hydrogen-Ion Concentration; Kinetics; Leishmania donovani; Mutation; Pentosyltransferases; Phosphoribosyl Pyrophosphate; Protein Multimerization; Protozoan Proteins; Pyrimidines; Recombinant Proteins; Spectrophotometry; Substrate Specificity; Temperature; Thiouracil; Uracil

Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) complexes of barbital, thiouracil, adenine, amino acids (methionine, lysine and alanine) and some mixed ligands were prepared and characterized by elemental analyses, IR, electronic spectra, magnetic susceptibility and ESR spectra. Coordination of the metallic centre to the oxygen and nitrogen atoms of barbital, thiouracil, amino acids and coordinate to amino group and nitrogen atom of adenine occurred. Electronic spectra and magnetic susceptibility measurements were utilized to infer the structure of the complexes which are octahedral for Mn(II), Fe(III), Co(II), Ni(II) and Cd(II) and tetrahedral for Mn(II), Cu(II), Zn(II) complexes. ESR spectra were observed for copper complexes with a d(x2)-(y2) ground state with small g(||) values indicating strong interaction between the ligands and their metal ions.

Topics: Adenine; Amino Acids; Barbital; Electrons; Ligands; Magnetics; Metals; Purines; Pyrimidines; Spectrophotometry, Infrared; Thiouracil

The condensation of 6-amino-2-thiouracil 1 with aromatic aldehydes afforded azomethine derivatives 3a,b. The formed azomethines underwent [4+2] cycloaddition with enaminones 4a-c and enaminonitrile 9 to form the corresponding condensed pyrimidines 8a-f and 11a,b, respectively. On the other hand, the interaction of 3a,b with acetylene derivatives 12a,b, 14 afforded the corresponding pyrido[2,3-d]pyrimidines 13a-d and 16a,b, respectively. The newly synthesized 2-azadiene 18 reacted with ortho-aminophenol and ortho-aminothiophenol 19a,b to yield the amidines 21a,b. The in vitro antimicrobial activity of some of the newly synthesized compounds was examined. All the tested compounds proved to be active as antibacterial and antifungal agents. Also the in vivo antitumor activity of compounds 8a, 11b, 13a,d, and 16b against lung (H460) and liver (HEPG2) carcinoma cells was examined. Compounds 8a, 16b showed moderate activity against lung carcinoma cell line (H460).

Topics: Antifungal Agents; Antineoplastic Agents; Drug Screening Assays, Antitumor; Gram-Negative Bacteria; Gram-Positive Bacteria; Humans; Liver Neoplasms; Lung Neoplasms; Microbial Sensitivity Tests; Molecular Structure; Pyrimidines; Structure-Activity Relationship; Thiouracil; Tumor Cells, Cultured

We have determined the X-ray structures of six MS2 RNA hairpin-coat-protein complexes having five different substitutions at the hairpin loop base -5. This is a uracil in the wild-type hairpin and contacts the coat protein both by stacking on to a tyrosine side chain and by hydrogen bonding to an asparagine side chain. The RNA consensus sequence derived from coat protein binding studies with natural sequence variants suggested that the -5 base needs to be a pyrimidine for strong binding. The five -5 substituents used in this study were 5-bromouracil, pyrimidin-2-one, 2-thiouracil, adenine, and guanine. The structure of the 5-bromouracil complex was determined to 2.2 A resolution, which is the highest to date for any MS2 RNA-protein complex. All the complexes presented here show very similar conformations, despite variation in affinity in solution. The results suggest that the stacking of the -5 base on to the tyrosine side chain is the most important driving force for complex formation. A number of hydrogen bonds that are present in the wild-type complex are not crucial for binding, as they are missing in one or more of the complexes. The results also reveal the flexibility of this RNA-protein interface, with respect to functional group variation, and may be generally applicable to other RNA-protein complexes.

Topics: Adenine; Bromouracil; Capsid; Capsid Proteins; Guanine; Levivirus; Models, Molecular; Nucleic Acid Conformation; Protein Conformation; Pyrimidines; RNA-Binding Proteins; RNA, Viral; Thiouracil

Topics: Animals; Carbon Dioxide; Carbon Isotopes; Cattle; Liver; Metabolism; Organ Size; Orotic Acid; Pharmacology; Pyrimidines; Rats; Research; RNA; Thiouracil; Thymine; Thymus Gland; Thyroid Gland; Uracil; Uracil Nucleotides

Topics: Escherichia coli; Pyrimidines; Thiouracil; Uracil

Topics: Barbiturates; Cytosine; Intestine, Small; Intestines; Pyrimidines; Thiouracil; Thymine; Uracil

The pyrimidine, 2-thiouracil, partly annuls the effect of photoperiodic induction in the short-day plant, Cannabis sativa L., when it is supplied at the onset of the dark period in quantities of 15-30 microg per plant. This treatment also produces aberrations in cellular differentiation in the leaves. Tracer studies show that 2-thiouracil becomes bound in cellular ribonucleic acid, which suggests that the effects on morphogenesis are due to interference with nucleic acid metabolism.

Topics: Cannabis; Cell Differentiation; Morphogenesis; Plants; Pyrimidines; Reproduction; Thiouracil

Topics: Animals; Goiter; Pyrimidines; Rats; Thiouracil