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Journal of Cellular Biochemistry 1985Azarts Chinese hamster ovary cells were 20 to 50 times more resistant to 8-azaguanine and 50 to 10 times more resistant to both 6-thioguanine and 6-mercaptopurine than... (Comparative Study)
Comparative Study
Metabolic properties of an azaguanine-resistant variant of Chinese hamster ovary cells (azarts) with normal levels of hypoxanthine-guanine phosphoribosyltransferase activity.
Azarts Chinese hamster ovary cells were 20 to 50 times more resistant to 8-azaguanine and 50 to 10 times more resistant to both 6-thioguanine and 6-mercaptopurine than wild-type cells. Resistance correlated with a failure of azarts cells to incorporate 8-azaguanine into the nucleotide pool and into nucleic acids. The uptake of hypoxanthine and guanine, on the other hand, was about the same in both types of cells and the hypoxanthine-guanine phosphoribosyltransferase of the azarts cells as measured in cell lysates was unaltered both in concentration and kinetic properties with hypoxanthine as well as 8-azaguanine as substrate. Plasma membrane permeability to 8-azaguanine and the regulation of intracellular pH were also not altered in azarts cells and there was no significant degradation of 8-azaguanine or azaguanine nucleotides. We conclude therefore that in azarts cells the phosphoribosylation of 8-azaguanine per se is specifically blocked but that this effect is abolished upon cell lysis.
Topics: Animals; Azaguanine; Biotransformation; Cells, Cultured; Cricetinae; Cricetulus; Drug Resistance; Female; Hypoxanthine; Hypoxanthine Phosphoribosyltransferase; Hypoxanthines; Ovary
PubMed: 3988817
DOI: 10.1002/jcb.240270205 -
Journal of Bacteriology Aug 1965
Topics: Azaguanine; Bacteriological Techniques; Culture Media; Drug Resistance; Drug Resistance, Microbial; Hydroxylamine; Hydroxylamines; Mycobacterium; Mycobacterium bovis; Mycobacterium tuberculosis; Pharmacology; Research
PubMed: 14329477
DOI: 10.1128/jb.90.2.556-557.1965 -
Biochimica Et Biophysica Acta Sep 19816-Mercaptopurine and 6-thioguanine strongly inhibited the zero-trans entry of hypoxanthine into Novikoff rat hepatoma cells which lacked hypoxanthine/guanine...
Facilitated transport of 6-mercaptopurine and 6-thioguanine and non-mediated permeation of 8-azaguanine in Novikoff rat hepatoma cells and relationship to intracellular phosphoribosylation.
6-Mercaptopurine and 6-thioguanine strongly inhibited the zero-trans entry of hypoxanthine into Novikoff rat hepatoma cells which lacked hypoxanthine/guanine phosphoribosyltransferase, whereas 8-azaguanine had no significant effect. 6-Mercaptopurine was transported by the hypoxanthine carrier with about the same efficiency as its natural substrates (Michaelis-Menten constant = 372 +/- 23 microM; maximum velocity = 30 +/- 0.7 pmol/microl cell H2O per s). 8-Azaguanine entry into the cells, on the other hand, showed no sign of saturability and was not significantly affected by substrates of the hypoxanthine/guanine carrier. The rate of entry of 8-azaguanine at 10-100 microM amounted to only about 5% of that of hypoxanthine transport and was related to its lipid solubility in the same manner as observed for various substances whose permeation through the plasma membrane is believed to be non-mediated. Only the non-ionized form of 8-azaguanine (pKa = 6.6) permeated the cell membrane. Studies with wild type Novikoff cells showed that permeation into the cell was the main rate-determining step in the conversion of extracellular 8-azaguanine to intracellular aza-GTP and its incorporation into nucleic acids. In contrast, 6-mercaptopurine was rapidly transported into cells and phosphoribosylated; the main rate-determining step in its incorporation into nucleic acids was the further conversion of 6-mercaptopurine riboside 5'-monophosphate.
Topics: Animals; Azaguanine; Biological Transport; Cell Membrane Permeability; Hydrogen-Ion Concentration; Hypoxanthine Phosphoribosyltransferase; Hypoxanthines; Liver Neoplasms, Experimental; Mercaptopurine; Rats; Thioguanine
PubMed: 7197551
DOI: 10.1016/0005-2736(81)90294-7 -
Nature Aug 1964
Topics: Aspergillus; Aspergillus nidulans; Azaguanine; Enzyme Inhibitors; Genetics; Nucleic Acids; Nucleotides; Proteins; Research
PubMed: 14202372
DOI: 10.1038/203506a0 -
Applied and Environmental Microbiology Sep 1978Eight mollicellins (depsidones) were assayed for mutagenicity and antibacterial activity in Salmonella/microsome tests involving histidine reversion and forward mutation... (Comparative Study)
Comparative Study
Eight mollicellins (depsidones) were assayed for mutagenicity and antibacterial activity in Salmonella/microsome tests involving histidine reversion and forward mutation to 8-azaguanine resistance. Two of them, mollicellins C and E, which contain a 3-methylbutenoic acid moiety, were mutagenic and bactericidal for Salmonella typhimurium in the absence of microsomes. Mollicellins D and F, each containing a chlorine atom, were bactericidal but not mutagenic. The mutagenic activity was completely abolished and the antibiotic activity was greatly reduced by coincubation with rat liver microsomes.
Topics: Animals; Anti-Bacterial Agents; Anti-Infective Agents; Ascomycota; Azaguanine; Chaetomium; Chemical Phenomena; Chemistry; Drug Resistance, Microbial; Histidine; Microsomes, Liver; Mutagens; Mutation; Mycotoxins; Rats; Salmonella typhimurium
PubMed: 365106
DOI: 10.1128/aem.36.3.412-420.1978 -
Journal of Cellular Physiology Feb 1973
Topics: Animals; Azaguanine; Cell Line; Clone Cells; Cricetinae; Culture Techniques; Cytological Techniques; Female; Genetic Variation; Guanine; Hypoxanthines; Mutation; Ovary; Pentosyltransferases
PubMed: 4568377
DOI: 10.1002/jcp.1040810112 -
Journal of Bacteriology Feb 1968An 8-azaguanine-resistant mutant, azg-11, derived from a guanine auxotroph, gua-1, of Salmonella typhimurium was isolated. This mutant was resistant to the analogue when...
An 8-azaguanine-resistant mutant, azg-11, derived from a guanine auxotroph, gua-1, of Salmonella typhimurium was isolated. This mutant was resistant to the analogue when grown on 2,6-diaminopurine, but showed greater susceptibility than the parent on guanine. Studies with the uptake of radioactive purines revealed that the mutant was defective in a mechanism for incorporation of guanine as well as of xanthine. Initial rates of uptake were determined for guanine at concentrations which were sufficiently low to make permeases limiting. The affinity constant K(m) for the mutant was found to be 2.5 x 10(-4)m; that of the parent was 2.3 x 10(-5)m. Examination of cell-free extracts suggested that the purine nucleotide pyrophosphorylases, responsible for the conversion of free intracellular purines to the corresponding nucleotides, were present and unaltered. The results indicate that the mutant is defective in a mechanism for the active transport for guanine and possibly xanthine.
Topics: Adenine; Azaguanine; Biological Transport; Carbon Isotopes; Drug Resistance, Microbial; Genetics, Microbial; Guanine; Molecular Biology; Mutation; Salmonella typhimurium; Xanthines
PubMed: 4867741
DOI: 10.1128/jb.95.2.458-464.1968 -
Applied Microbiology Oct 1968With (14)C-tagged 8-azaguanine and guanine in a Bushnell-Haas medium with glucose as a carbon source, the rate of incorporation of the two bases was determined in...
With (14)C-tagged 8-azaguanine and guanine in a Bushnell-Haas medium with glucose as a carbon source, the rate of incorporation of the two bases was determined in Cladosporium resinae. There was a marked preference for the incorporation of 8-azaguanine over guanine.
Topics: Azaguanine; Carbon Isotopes; Guanine; Mitosporic Fungi; Nucleic Acids
PubMed: 5693345
DOI: 10.1128/am.16.10.1454-1456.1968 -
Nature Aug 1981Indirect evidence implies that 8-azaguanine-resistant (AGr) lymphocytes in human peripheral blood are mutants associated with the loss of the hypoxanthine-guanine...
Indirect evidence implies that 8-azaguanine-resistant (AGr) lymphocytes in human peripheral blood are mutants associated with the loss of the hypoxanthine-guanine phosphoribosyltransferase (HPRT) locus on the active X chromosome, the mutation frequency increasing linearly with age. AGr variants are readily induced in lymphocytes exposed to mitomycin C in vitro, their incidence correlating with induced sister chromatid exchanges (SCEs). Although SCE events and the development of an AGr phenotype may reflect a common type of DNA damage, mitomycin C-induced Agr variants are not mutants but are suggested to be cells having a transcriptional block at the HPRT locus. AGr variants are also readily induced by X rays in vitro, their incidence correlates closely with the incidence of aberrations induced in the X chromosome and they are considered to have a mutational origin.
Topics: Age Factors; Azaguanine; Cells, Cultured; Crossing Over, Genetic; Drug Resistance; Humans; Lymphocytes; Mitomycins; Mutation; Sex Factors; Sister Chromatid Exchange; X-Rays
PubMed: 7254356
DOI: 10.1038/292601a0 -
Mutation Research Mar 1976Asynchronous Chinese hamster ovary cells were irradiated and colony survival in Alpha MEM medium with dialyzed serum was determined with or without 15 mug/ml...
Asynchronous Chinese hamster ovary cells were irradiated and colony survival in Alpha MEM medium with dialyzed serum was determined with or without 15 mug/ml 8-Azaguanine (AG). Data indicated that a reproducible assay for the system was dependent upon controlling cell density at least two days prior to induction as well as throughout the expression period. Generally, spontaneous and radiation-induced mutant frequencies decreased when cell densities exceeded a critical density of 3-6 X 10(4) cells/cm2. Infrequently, the critical density was exceeded by a factor of two with no observed decrease, possibly correlated with a longer cell doubling time. Drug depletion artifacts can occur because of drug degradation, or because wild-type cells utilize the drug or produce conditions which reduce uptake of the drug. Thus, as the effective drug concentration is lowered, the observed mutant frequency increases because a spectrum of mutants resistant to only low concentrations can now survive. In fact, refeeding with AG at intervals during the incubation period lowered spontaneous and radiation-induced frequencies approx. 5-fold. Therefore, to standardize conditions, cells were trypsinized at the end of the expression time and replated at a constant cell number for mutant selection by AG. Over two generations of growth during the expression period were required for optimal manifestation of induced mutants, and when densities were kept below 4 X 10(4) cells/cm2 at all times, observed mutant frequencies did not change significantly over a period between 80 and 140 h post-induction (over 4 generations for irradiated cells and over 6 generations for controls). Previous reports of observed mutant frequencies decreasing beyond three generations may be due to cell interaction prior to mutant selection.
Topics: Azaguanine; Cell Count; Cell Division; Clone Cells; Dose-Response Relationship, Drug; Dose-Response Relationship, Radiation; Drug Resistance; Mutation; Radiation Genetics; X-Rays
PubMed: 1264110
DOI: 10.1016/0027-5107(76)90222-0