• R K Bhattacharya

      Articles written in Journal of Biosciences

    • Functional changes in rat liver tRNA following aflatoxin B1 administration

      R K Bhattacharya V S Aboobaker

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      Administration of aflatoxin B1 (3 mg/kg body wt) to rats leads to strong inhibition of the acceptor activity of liver tRNA as measured by charging with [14C]-chorella protein hydrolysate. The maximum inhibition occurs 2 h after treatment. At increasing intervals after treatment, the inhibition appears to be gradually relieved, till control values are restored by 72 h. The charging experiment using several [14C]-amino acids separately shows pronounced inhibition of acceptor activity of all tRNA species, although the degree of inhibition varies with individual species. Preliminary results seem to rule out the possibility of hypermethylation of tRNA or damage to the CCA terminus as probable causes. The resultant functional changes may be attributed to a covalent interaction of aflatoxin B1-metabolite with tRNA.

    • Inhibition ofin-vitro amino acid incorporation by the carcinogen N-methyl N’-nitro N-nitrosoguanidine

      R S Bagewadikar R K Bhattacharya

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      The addition of the carcinogen, N-methyl N’-nitro N-nitrosoguanidine, to a cell-free system consisting of purified polysome and ‘pH 5 enzyme’ fraction resulted in a marked inhibition of incorporation of (14C)-leucine into polypeptides. The extent of inhibition was remarkably high if the cell-free system contained limiting amount of ‘pH 5 enzyme’ fraction. Under this condition, the rate of inhibition was dependent on the concentration of carcinogen. Some component present in the ‘pH 5 enzyme’ fraction was inferred to be the susceptible factor, since the inhibition at low concentration of carcinogen could be reversed by increasing the amount of this fraction in the polysomal system. It was ascertained that tRNA was the primary target of carcinogenic action. Evidence suggested that functions attributed to tRNA such as aminoacylation and ribosomal transfer were both affected in a characteristic way by the action of the carcinogenic N-nitroso compound.

    • In vivo effect of L-ascorbic acid on benzo(α)pyrene metabolite-DNA adduct formation in rat liver

      G M Shah R K Bhattacharya

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      Pretreatment of male Wistar rats with L-ascorbic acid results in a decrease in thein vivo covalent binding of benzo(a)pyrene to hepatic nuclear DNA.In vitro formation of this adduct is also found to be low in liver slices and in liver nuclei of pretreated rats. No inhibition of the adduct formation is, however, observed when benzo (a) pyrene and exogenous DNA are incubated with liver microsomes isolated from ascorbic acid treated rats.It appears that the presence of ascorbate in the cellular or subcellular environment is essential for its inhibitory action.

    • Phosphoinositide signal transduction pathway in rat liver mitochondria

      K Pasupathy M Krishna R K Bhattacharya

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      Phosphorylation of endogeneous phosholipids of rat liver mitochondrial fractions with γ[32P]ATP revealed formation of all the known inositol phospholipids, such as phosphatidylinositol, phosphatidylinositol phosphate and phosphatidylinositol bisphosphate. Additionally, a new inositol phospholipid was detected. Incorporation of [3H]-labelled insositol followed a similar profile. Enzymatic experiments indicated that the new lipid could possibly be phosphatidylinositol trisphosphate. The presence of phosphoinositides-generated second messengers such as diacylglycerol and inositol trisphosphate was also confirmed. Protein kinase C, which acts as mediator between second messengers and nuclear factors, was also found to be present in mitochondria in significant amount. These results suggest that phosphoinositide signal transduction pathway is operative in rat liver mitochondria.

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