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  • 1
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The physiological action of extracellular ATP and other nucleotides in the nervous system is controlled by surface-located enzymes (ecto-nucleotidases) of which several families with partially overlapping substrate specificities exist. In order to identify ecto-nucleotidases potentially associated with neural cells, we chose PC12 cells for analysis. PC12 cells revealed surface-located ATPase and ADPase activity with apparent Km-values of 283 µm and 243 µm, respectively. Using PCR we identified the mRNA of all members of the ecto-nucleoside triphosphate diphosphohydrolase family investigated (NTPDase1 to NTPDase3, NTPDase5/6), of ecto-nucleotide pyrophosphatase/phosphodiesterase3 (NPP3), tissue-non-specific alkaline phosphatase and ecto-5′-nucleotidase. The surface-located catalytic activity differed greatly between the various enzyme species. Our data suggest that hydrolysis of ATP and ADP is mainly due to members of the ecto-nucleoside triphosphate diphosphohydrolase family. Activity of ecto-5′-nucleotidase and alkaline phosphatase was very low and activity of NPP3 was absent. For a detailed analysis of the cellular distribution of ecto-nucleotidases single and double transfections of PC12 cells were performed, followed by fluorescence analysis. Ecto-nucleotidases were distributed over the entire cell surface and accumulated intracellularly in varicosities and neurite tips. PC12 cell ecto-nucleotidases are likely to play an important role in terminating autocrine functions of released nucleotides and in producing extracellular nucleosides supporting the survival and neuritic differentiation of PC12 cells.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0983
    Keywords: Multi-copy plasmid ; Hyper-resistance ; 4-NQO ; MNNG ; Triaziquone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Screening of a multi-copy vector-based yeast genomic library in haploid cells of wild-type Saccharomyces cerevisiae yielded transformants hyper-resistant to various chemical mutagens. Genetical analysis of the yeast insert DNAs revealed three genes SNG1, SNQ2, and SNQ3 that confer the phenotype hyper-resistance to MNNG, to 4-NQO and triaziquone, and to mutagens 4-NQO, MNNG, and triaziquone, respectively. Integration of the gene disruption-constructs into the haploid yeast genome yielded viable null-mutants with a mutagen-sensitive phenotype. Thus, copy number of these non-essential yeast genes determines the relative resistance to certain chemical mutagens, with zero copies yielding a phenotype of mutagen sensitivity and multiple copies one of mutagen hyper-resistance, respectively.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1617-4623
    Keywords: Mutagen hyper-resistance ; 4-nitroquinolineN-oxide ; Yeast ; ATP-dependent permease
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The yeast gene SNQ2 confers hyper-resistance to the mutagens 4-nitroquinoline-N-oxide (4-NQO) and Triaziquone, as well as to the chemicals sulphomethuron methyl and phenanthroline when present in multiple copies in transformants of Saccharomyces cerevisiae. Subcloning and sequencing of a 5.5 kb yeast DNA fragment revealed that SNQ2 has an open reading frame of 4.5 kb. The putative encoded polypeptide of 1501 amino acids has a predicted molecular weight of 169 kDa and has several hydrophobic regions. Northern analysis showed a transcript of 5.5 kb. Haploid cells with a disrupted SNQ2 reading frame are viable. The SNQ2-encoded protein has domains believed to be involved in ATP binding and is likely to be membrane associated. It most probably serves as an ATP-dependent permease.
    Type of Medium: Electronic Resource
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