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Release of nucleotide-cleaving phosphatase from carrot cell grown in suspension culture.
No full textHigher plants contain unspecific phosphatases which can hydrolyse a wide variety of phosphate esters including sugar phosphates, nucleotides and phosphoenolpyruvate (Shaw 1966, Matile 1975). These enzymes can be released by plant tissue culture into the
culture medium (Straus and Campbell 1963). Also terminal pyrophosphate bonds are hydrolysed by these enzymes (Shaw 1966, Hirasawa et al. 1979). While studying polydeoxyribonucleotide synthesis in cultured carrot cells it was found that deoxyribonucleoside 5'-triphosphates were hydrolysed and used as DNA precursors by intact cells at a rate approaching that of deoxyribonucleotides. This behaviour is different from that of bacteria
and mammalian cells which are not able to rapidly utilize exogenous deoxyribonucleotides as DNA precursors. In this report we show that phosphohydrolases are excreted into the medium by carrot cell suspension cultures, and thus they are responsible for a rapid transformation of nucleotides into permeable compounds,
which can be taken up by the cell and incorporated into DNA
Effect of nalidixic acid and novobiocine on the metabolism of suspension cultured carrot cells
No full textSuspension cells of Daucus carota L., cv Lunga di Amsterdam are extremely sensitive to both nalidixic acid and novobiocine. The synthesis of DNA, RNA and protein are inhibited within minutes of exposure even at concentrations less than 0.1 mM of both drugs. Moreover, uptake of deoxythymidine by cells is impaired more severely than by sodium azide. Reduction of oxygen consumption caused by the two drugs is slower than in the case of NaN, and occurs a few minutes after the inhibition of macromolecular biosynthesis. This excludes the possibility that the block in oxidation is the
primary cause of the observed inhibition of cellular functions and suggests that the inhibition of ATP synthesis, which is immediately affected in both cases, may be responsible for these effects. A possible interaction with other cellular targets may be secondary to the uncoupling effect. Cell growth is completely inhibited by 0.3 mM
concentration of both drugs, but this inhibition is irreversible only in the case of novobiocine. The irreversibility of cell growth inhibition by novobiocine can be explained by the total disappearance of ATP from the cell
Properties of the high molecular weight deoxyribonuclease of Bacillus subtilis degrading single stranded DNA.
No full text
A simplified procedure for the analysis of DNA polymerase III levels in Bacillus subtilis strains.
No full textBacillus subtilis deoxyribonuclease activity specific for single stranded deoxyribonucleic acid: cellular site and variation during germination and sporulation.
No full textQuinolone binding to DNA is mediated by magnesium ions
No full textThe binding of plasmid DNA to norfloxacin, a quinolone antibacterial agent, was investigated by fluorescence, electrophoretic DNA unwinding, and affinity chromatography techniques. The amount of quinolone bound to DNA was modulated by the concentration of Mg2+. No interaction was evident in the absence of Mg2+ or in the presence of an excess of Mg2+, whereas maximum binding was observed at a Mg2+ concentration of 1-2 mM. The experimental data can be fitted to the formation of three types of Mg adducts: a binary adduct with norfloxacin and Mg2+, a binary adduct with DNA and Mg2+, and a ternary adduct with quinolone, plasmid, and Mg2+. We propose a model for the ternary complex, in which Mg acts as a bridge between the phosphate groups of the nucleic acid and the carbonyl and carboxyl moieties of norfloxacin. Additional stabilization may arise from stacking interactions between the condensed rings of the drug and DNA bases (especially guanine and adenine), which may account for the preference exhibited by quinolones for single-stranded and purine-rich regions of nucleic acids. Other possible biochemical pathways of drug action are suggested by the observation that norfloxacin binds Mg2+ under conditions that are close to physiological
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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