• Chanchal K Mitra

      Articles written in Journal of Biosciences

    • Photoproduction of hydrogen by photosynthetic bacteria from sewage and waste water

      M Sunita Chanchal K Mitra

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      Numerous prokaryotes, belonging to physiologically and taxonomically different groups, are able to produce hydrogen. Some photosynthetic bacteria have the property of light-dependent production of hydrogen from organic substrates. We isolated several photosynthetic purple and green bacteria from enrichment cultures made from the water of a waste-water pond of a cool-drink refilling station. After testing them for their ability to use various organic compounds as carbon source, and sulphide, thiosulphate and organic compounds as electron donor, we selected the fastest-growing isolate, aRhodopseudomonas, for a study of its ability to produce molecular hydrogen in presence of light. Immobilized cells of this isolate produced significant amounts of hydrogen from both sewage and waste water

    • Protein sequences as random fractals

      Chanchal K Mitra Meeta Rani

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      The analysis of primary sequences from a protein sequence data base suggests that the sequences can be considered as examples of constrained random fractals. Fractal dimensions of the positional distributions of the 20 residues along the chain have been calculated. These fractal dimensions can be used as indices of intrinsic preferences of various residues.

    • Periodicities in protein sequences

      Meeta Rani Chanchal K Mitra

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      The correlation between various amino acid residues (either same or different), along the polypeptide chain have been studied using a large data base. A table of preference values for pairs having strong correlations has been constructed, which can be used to study any sequence and by calculating the weight of these sequences based on these preference values, a rough distinction between a “natural” and a “random” sequence can be made, One can further comment on the evolutionary status of proteins based on these weights.

    • Correlation analysis of frequency distributions of residues in proteins

      Meeta Rani Chanchal K Mitra

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      Autocorrelation and spectrum analyses of amino acid residues along protein chains in a large data base has been performed. Results reveal the presence of general long range correlations. Similar analyses of simulated (random) peptides do not exhibit any such long range correlations. Based on the results of nur analysis, an attempt has been made to model the distribution of residues in protein sequences on a fractional Brownian motion and individual sequences as multi-fractals. For this purpose, the characteristics of an fractional Brownian motion namely, the scaling parameterH. the spectral exponent β and the fractal dimensionD, have been described

    • Proteins as special subsets of polypeptides

      Meeta Rani Chanchal K Mitra M Cserzo I Simon

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      A large protein sequence database with over 31,000 sequences and 10 million residues has been analysed. The pair probabilities have been converted to entropies using Boltzmann’s law of statistical thermodynamics. A scoring weight corresponding to “mixing entropy” of the amino acid pairs has been developed from which the entropies of the protein sequences have been calculated. The entropy values of natural sequences are lower than their random counterparts of same length and similar amino acid composition. Based on the results it has been proposed that natural sequences are a special set of polypeptides with additional qualification of biological functionality that can be quantified using the entropy concept as worked out in this paper.

    • Covalent enzyme immobilization onto glassy carbon matrix-implications in biosensor design

      P Sree Divya D Savitri Chanchal K Mitra

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      The aim of the present work is to design an electrode for biosensors by covalent immobilization of the redox enzyme. In the covalently modified electrode, the biocatalyst is located close to the electrode surface and this is expected to enhance the electron transfer rate from the enzyme to the electrode. Several methods of covalent immobilization of enzymes onto a glassy carbon surface are described. We have chosen horse radish peroxidase enzyme in our study but any other suitable enzyme can be immobilized depending on the intended use. A three step procedure that includes (i) heat treatment of matrix at l00-l10°C to remove volatiles and absorbates, (ii) chemjcal pretreatment to introduce functional groups like -OH, -NO2, -Br etc. followed by (iii) glutaraldehyde coupling of the enzyme (for the nitrated matix after subsequent reduction) or modification of the matrix by carboxymethylation and enzyme coupling using carbodiimide (for hydroxylated matrix) was followed. The amount of enzyme immobilized onto the carbon surface was estimated by spectrophotometric enzymatic activity assay, commonly used for the soluble enzyme. We found that simple nitration did not introduce any significant amount of functional groups and the matrix with hydrogen peroxide pretreatment showed the highest enzyme loading of 0.05 U/mg of carbon matrix. The HRP enzyme electrode was tested in a rotating disk experiment for its response with the substrate.

    • Role of mediators in electron transport from glucose oxidase redox centre to electrode surface in a covalently coupled enzyme paste electrode

      D Savitri Chanchal K Mitra

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      We have studied the glucose oxidase immobilized carbon paste electrodes in the presence and absence of small mediator molecules. We have used p-benzoquinone and riboflavin as mediators in our studies. The effect of mediator molecules on the electron transfer between the enzyme redox centre and the electrode surface was explained from the cyclic voltammograms and rotating disk electrode data. In the absence of oxygen, we have noted that the mediators play a central role in the electron transfer. We have also proposed a possible mechanism for the electron transfer from enzyme active site to the electrode surface via mediators, based on our observations.

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