• P Maruthi Mohan

      Articles written in Journal of Biosciences

    • 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.

    • Excretion of pyruvate in nickel toxicity in wild type and Ni2+ resistant mutants ofNeurospora crassa

      P Maruthi Mohan K Sivarama Sastry

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      The parent wild strainNeurospora crassa Em 5297a and three Ni2+ resistantNeurospora crassa mutants have been shown to excrete pyruvate into the culture medium in Ni2+ and Co2+ toxicities. Ni2+ has a more pronounced effect in this regard. The excretion is progressive with growth inhibition and is abolished by Mg2+ in all strains and by Fe3+ partially in the Em strain but not inNeurospora crassa NiR1. Pyruvate, citrate and malate supplementation reverse growth inhibition caused by excess Ni2+, but with concomitant suppression of Ni2+ accumulation. It is suggested that one of the features of Ni2+ toxicity inNeurospora crassa is a derangement in carbohydrate metabolism at step(s) beyond pyruvate and that this is possibly due to decreased invivo activity of Mg2+ dependent processes

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