• G K Khuller

      Articles written in Journal of Biosciences

    • Effect of environmental factors on the limpid composition membrane structure and permeability ofMicrosporum gypseum

      Dipak Kapur Rakesh Pandey Seema Vaidya G K Khuller

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      Supplementation with unsaturated fatty acids, substitution of glucose by glycerol as carbon source and lowered growth temperature (20°C) increased the total phospholipid content ofMicrosporum gypseum spheroplasts. Levels of sterols increased with glycerol substitution and decreased in other growth conditions. Substantial changes were seen in the ratios of unsaturated to saturated fatty acids and phosphatidylcholine to phosphatidylethanolafne under all the experimental conditions. Changed lipid composition resulted in altered uptake of amino acids (L-lysine, L-aspartic acid and L-glycine) and increased number of binding sites for a fluorescent probe, 1-anilinonaphthalene-8-sulfonate.

    • Effect of altered sterol levels on the transport of amino acids and membrane structure ofMicrosporum gypseum

      Seema Vaidya Geeta Bharti Rakesh Pandey G K Khuller

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      Ergosterol and cholesterol supplementation resulted in a significant increase (1·5-fold) in the sterol content while phospholipid remained unaffected inMicrosporum gypseum. The levels of phosphatidylethanolamine and phosphatidylcholine increased in ergosterol supplemented cells. However, a decrease in phosphatidylcholine and an increase in phosphatidylethanolamine was observed in cholesterol grown cells. The ratio of unsaturated to saturated fatty acids decreased on ergosterol/cholesterol supplementation. The uptake of amino acids (lysine, glycine and aspartic acid) decreased in sterol supplemented cells. Studies with fluorescent probe l-anilinonaphthalene-8-sulfonate showed structural changes in membrane organisation as evident by increased number of binding sites in such cells.

    • Phospholipids of ethambutol-susceptible and resistant strains ofMycobacterium smegmatis

      Monika Sareen G K Khuller

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      The composition, subcellular distribution and rate of synthesis of phospholipids were compared in ethambutol susceptible and resistant strains ofMycobacterium smegmatis. Significant quantitative alterations in phospholipids accompanied the acquisition of resistance, whereas fatty acyl group composition of total phospholipid remained the same in ethambutol resistant and susceptible strains. Cell wall of resistant strain exhibited an accumulation of phospholipids and a decrease in the degree of unsaturation of phospholipid fatty acyl groups. Changes in the cell wall phospholipid composition may contribute to resistance ofMycobacterium smegmatis to ethambutol.

    • Biochemical studies with bi-resistant mutants (ethambutol plus streptomycin and isoniazid plus streptomycin) ofMycobacterium smegmatis ATCC 607

      Kavita Kanwar G K Khuller

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      Biochemical characteristics of bi-resistant mutants (resistant to ethambutol plus streptomycin or isoniazid plus streptomycin) of mycobacteria isolated by replica plating fromMycobacterium smegmatis ATCC were compared with those of the drug-susceptible strains. Reduced incorporation of [14C]uracil, [3H]lysine and [14C]acetate into RNA, protein and phospholipids respectively was seen in the resistant mutants. Total phosphorlipids were enhanced in ethambutol plus streptomycin resistant mutant and decreased in isoniazid plus streptomycin resistant mutant. There were similar changes in levels of individual phospholipids. The resistant mutants revealed an accumulation of phospholipids in the cell wall, and a marked decrease of phospholipids in the cell membrane in comparison to the susceptible strain. Several qualitative alterations in the polypeptide profile (with respect to number and molecular weight) of the crude protein extract and of different subcellular compartments were seen in the resistant mutants.

    • Effect of griseofulvin on lipid composition and membrane integrity inMicrosporum gypseum

      Indu Bala Chugh M P Gupta G K Khuller

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      The effect of griseofulvin on lipid constituents and membrane permeability ofMicrosporum gypseum has been investigated. Mycelia grown in medium containing griseofulvin (IC50 concentration) possessed a lower content of total lipids, phospholipids and sterols. This inhibitory effect was further supported by decreased incorporation of [14C] acetate in total lipids, total phospholipids and sterols. Decrease in total phospholipids was also reflected to a varying extent in all individual phospholipids. An increase in the unsaturated to saturated fatty acid ratio was observed in mycelia grown in medium containing griseofulvin. Membrane permeability was affected by griseofulvin as shown by increased K+-efflux and greater leakage of intracellular [32P] labelled components from prelabelled cells. Our results suggest that the antifungal activity of griseofulvin is partially due to its secondary effect on lipid constituents ofMicrosporum gypseum.

    • Regulation of phospholipid synthesis inMycobacterium smegmatis by cyclic adenosine monophosphate

      Monica Sareen Harpinder Kaur G K Khuller

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      Forskolin, an adenylate cyclase activator and a cyclic AMP analogue, dibutyryl cyclic AMP have been used to examine the relationship between intracellular levels of cyclic AMP and lipid synthesis inMycobacterium smegmatis. Total phospholipid content was found to be increased in forskolin grown cells as a result of increased cyclic AMP levels caused by activation of adenylate cyclase. Increased phospholipid content was supported by increased [14C] acetate incorporation as well as increased activity of glycerol-3-phosphate acyltransferase. Pretreatment of cells with dibutyryl cyclic AMP had similar effects on lipid synthesis. Taking all these observations together it is suggested that lipid synthesis is being controlled by cyclic AMP in mycobacteria.

    • Immunoprophylactic studies on cell wall associated proteins ofMycobacterium tuberculosis H37Ra

      Neelam Dhiman Indu Verma G K Khuller

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      The cell wall protein peptidoglycan complex (CW-PPC) ofMycobacterium tuberculosis H37Ra was isolated through sequential extraction of lipids, carbohydrates and soluble proteins. CW-PPC emulsified in FIA was found to induce significant protection in mice against challenge with LD50 dose ofM. tuberculosis H37Rv. To identify the immunoprotective components of CW-PPC, the proteins in avid association with peptidogican were dissociated by chemical treatment with trifluoromethanesulthonic acid (CF3CO3H): anisole (2:1). Immunoreactivity of total (CW-Pr) as well as its component proteins i.e., 71, 60 and 45 kDa proteins of cell wall was studied in animals immunized with CW-Pr-FIA. The 71 kDa protein was found to be most immunoreactive giving higher T-cell sensitization and humoral responses. Further, immunization of mice with 71 kDa-FIA demonstrated enhanced T- and B- cell responses. Mice immunized with 71 kDa-FIA gave significantly higher protection (P ≤ 0.05) against intravenous challenge with LD50 dose ofM. tuberculosis H37Rv, than BCG immunized animals. The results indicate the potential of 71 kDa cell wall protein as a suitable candidate for Cthe subunit vaccine.

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