• J Nirmala

      Articles written in Journal of Biosciences

    • Beryllium toxicity inNeurospora crassa

      A Naidu J Nirmala K Sivarama Sastry

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      InNeurospora crassa,0.44 mM Be2+ caused half-maximal inhibition of growth and this inhibition could be fully counteracted by the addition of 2.5 mM Ca2+ to the medium. Mn2+ and Mg2+ were less effective in reversing the growth inhibition caused by Be2+ and the order of effectiveness was Ca2+ > Mn2+ > Mg2+. Fe3+ and Zn2+ were ineffective in reversing Be2+ toxicity.

      Pyruvate, malate and succinate also reversed the growth inhibition caused by Be2+ inN. crassa. Pyruvate restored growth by a mechanism not involving control of Be2+ accumulation in the mould. The rate of utilisation of glucose by the mycelia grown in the presence of Be2+ was reduced, while that of pyruvate was not affected. The results indicate that the primary metabolic lesion in Be2+ toxicity inN. crassa is probably a block at some step(s) in the glycolytic sequence.

    • A specific effect of copper on methylene blue sensitized photodegradation of nucleic acid derivatives

      P Maruthi Mohan J Nirmala K Sivarama Sastry

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      Among several metal ions tested, Cu2+ was unique in slowing down methylene blue sensitized photodynamic breakdown of some nucleic acid bases and nucleosides. The t1/2 values were increased in the case of xanthine and uric acid by Cu2+, but without any alteration in the nature or amounts of photoproducts formed. Xanthine was degraded quantitatively to allantoin and urea.

      The breakdown of the sugar moiety of nucleosides was more drastically retarded than that of the purine ring. The decomposition rate and its magnitude was dependent on the concentration of Cu2+ as well as the nucleoside. The most profound increase in t1/2 values was found with xanthosine—7 min for the purine ring and 65 min for the ribose moiety, at 0.6 mM Cu2+ Hg2+ in the case of xanthine, and some paramagnetic metal ions in the case of the nucleosides, slowed down the photobreakdown to a small extent; however, differential effects were not observed unlike with Cu2+. None of the other metal ions tested significantly influenced the process.

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