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Biomedical subjects

D Bhattacharyya

Publications and source records attributed to D Bhattacharyya.

87 records · Page 5Linked to original sources
PubMed1986

Role of selective pressure by screening organisms in the development of producer mutant isolates of different antibiotic markers.

The phenotypes of producer mutant isolates when obtained after mutagenesis of the spontaneous degenerate Aspergillus versicolor N5 by screening on Trichophyton rubrum and those on A. niger G3Br were found to be markedly different. In respect of phenotypic character anti-T. rubrum producer mutant isolates resembled the parental type more closely (which is specifically active against T. rubrum and generally against dermatophytes) than anti-A. niger mutant isolates. This clearly indicates not only the role of selective pressure of the screening organism in the development of a given producer mutant isolate but also shows the possibility of recovery of a producer type of the lost antibiotic marker.

Anti-Bacterial Agents↗
PubMedDate not supplied

Structural basis of DNA recognition by anticancer antibiotics, chromomycin A(3), and mithramycin: roles of minor groove width and ligand flexibility.

Anticancer antibiotics, chromomycin A(3) (CHR) and mithramycin (MTR), inhibit cellular processes like transcription and replication, by binding reversibly to double-stranded DNA via minor groove, in the presence of bivalent metal ions like Mg(2+) with GC base specificity. Here, we have attempted to assess the roles of two parameters-namely DNA groove dimension and flexibility of the ligand-in the structural recognition between the ligands, (drug)(2)Mg(2+) and DNA. For the purpose we have employed three synthetic oligonucleotides with minor groove width lying between B- and A-type structures as model DNA sequences: d(GCGCGCGC)(2) in B-form, d(CCGGCGCCGG)(2) in B-form with unusual wide minor groove, and (GGGGCCCC)(2) in A-form. Association of the (drug)(2)Mg(2+) with the oligomers have been probed using spectroscopic techniques like absorbance, fluorescence, and CD. The binding and thermodynamic parameters for the different association processes have also been characterized. Major conclusions from the above studies are as follows. Groove size of the oligomers influences the conformation of the bound ligand. A saccharide dependent variation in structural rigidity of the ligands, (MTR)(2)Mg(2+) and (CHR)(2)Mg(2+), has been observed that leads to differences in the energetics of recognition of the same DNA sequence by the two ligands. In contrast to (CHR)(2)Mg(2+), higher flexibility in (MTR)(2)Mg(2+) makes its conformation in the DNA bound form less sensitive to the groove dimension of DNA.

Antibiotics, Antineoplastic↗
PubMedDate not supplied

Activity studies of immobilized subtilisin on functionalized pure cellulose-based membranes.

The activity of immobilized subtilisin BPN' on pure cellulose-based membrane support was investigated using site-directed and random immobilization approaches. The catalytic activity of site-directed immobilized subtilisin on pure cellulose fiber-based materials was found to be 81% of that in homogeneous solution, while that of randomly immobilized subtilisin was 27%. Pure cellulose membrane supports provided large surface areas for high enzyme loading without diffusional limitations. The activity of immobilized subtilisin on pure cellulose support was more than twice that on a modified polyether sulfone (MPS) membrane, which was attributed to the higher hydrophilicity of cellulose. Immobilized subtilisin maintained its initial activity for 14 days at 4 degrees C and 7 days at 24 degrees C. The immobilized enzyme could resist higher temperature and operate over a wider range of pH without loss of activity. This study showed that pure cellulose fiber-based membranes are well suited for enzyme immobilization and biocatalysis.

Affinity Labels↗
PubMedDate not supplied

Selective isolation and purification of tat protein via affinity membrane separation.

This work deals with the separation of Tat protein from a complex fermentation broth using an affinity membrane system. Tat is a regulatory protein that is critical for HIV-1 replication and thus a potential candidate for vaccine and drug development. Furthermore, Tat can facilitate transport of exogenous molecules across cell membranes and is implicated in pathogenesis of HIV dementia. Affinity membranes were prepared through coupling of avidin within a 4-stack membrane construct. Tat (naturally biotinylated) accessibility in the bacterial lysate feed was influenced by the presence of RNAse, protein concentration, and ionic strength. Enhanced accessibility translated to a marked increase in the overall product yield per pass. The purity of the membrane-isolated Tat was compared to that prepared via packed column chromatography through SDS-PAGE, Western blot, activity assay, and neurotoxicity studies. Tat protein produced via membrane separation yielded primarily monomeric forms of the oligopeptide sequence, whereas column chromatography produced predominately polymeric forms of Tat. These differences resulted in changes in the neurotoxicity and cellular uptake of the two preparations.

Blotting, Western↗
PubMedDate not supplied

Kinetics and active fraction determination of a protease enzyme immobilized on functionalized membranes: mathematical modeling and experimental results.

A detailed study on the performance of a membrane bioreactor is presented, considering diffusion reaction models with product adsorption and structure-function correlations. The enzyme papain was utilized for experimental investigation both in the homogeneous state and on a modified polysulfone (MPS) membrane. Variation of enzyme loading on the membrane and enzyme concentration in the solution state depicted decreasing activity with increasing loading. The performance of the bioreactor was simulated using a diffusion reaction model within a recirculation loop. Electron paramagnetic resonance (EPR) spectroscopy was utilized to study the conformational changes of the active site of papain immobilized on the MPS membrane. Two models were applied to correlate the structure and function of the biocatalyst, based on loading (kinetics) and EPR (structure). The active fractions, lambda, determined from the two models were 0.29 and in the range 0.25-0.3, respectively. The intrinsic kinetics (Vmax) for the immobilized enzyme as determined by the correlations were in the range 101-121 micromol/(g.min), compared to 111 micromol/(g.min) for the homogeneous enzyme. This proves that the immobilized enzyme kinetics do approach homogeneous kinetics for papain on the MPS membrane, when corrected for adsorption and conformational changes.

Catalysis↗
PubMedDate not supplied

Structural basis of DNA flexibility.

It has been recently shown by us, on the basis of crystal structure database that the flexibility of B-DNA double helices depends significantly on their base sequence. Our model building studies further indicated that the existence of bifurcated cross-strand hydrogen bonds between successive base pairs is possibly the main factor behind the sequence directed DNA flexibility. These cross-strand hydrogen bonds are, of course, weaker than the usual Watson-Crick hydrogen bonds and their bond geometry is characterized by relatively larger bond lengths and smaller bond angles. We have tried to improve our model structures by incorporating non-planarity of the amino groups in DNA bases due to the presence of lone pair electrons at the nitrogen atoms. Energy minimization studies have been carried out by using different quantum chemical methods, whereby it is found that in all cases of N-H....O type cross-strand hydrogen bonds, the bond geometry improves significantly. In the cases of N-H....N type hydrogen bonds, however, no such consistent improvements can be noticed. Perhaps the true picture would emerge only if all the other interactions present in the DNA macromolecule could be appropriately taken into account.

Crystallography↗
PubMedDate not supplied

Peptidyl transferase activity of tRNA: a quantum chemical study.

The mechanism of protein synthesis is still unknown due to inability to detect the so-called enzyme "peptidyl transferase" even after elucidation of high-resolution crystal structure of ribosome. We have recently shown by model building and semi-empirical energy calculation that the tRNA molecule at P-site of ribosome may act as peptidyl transferase (Das et al. (1999) J. Theor. Biol. 200, 193-205). We proposed that the tetrahedral intermediate formed from nucleophylic attack of CO of P-site amino-acylated tRNA by NH2 of A-site amino-acylated tRNA is converted to a six-member ring intermediate by conformational change. This ring intermediate produces a free tRNA and a tRNA covalently linked to a peptide. However, energy of the six-member ring intermediate was calculated to be quite high. We show here that the energy values of all the reactants, intermediates and products are within the expected range when they are calculated using high level ab initio quantum chemical methods.

Alanine↗
PubMedDate not supplied

B cell non-Hodgkin cerebral lymphoma associated with an anaplastic oligodendroglioma.

Primary central nervous system lymphomas and anaplastic oligodendrogliomas are not uncommon; however, no association between the 2 has been documented to date. We describe a unique case, whereby a patient presenting with seizures and slight impairment of higher functions, underwent frontal lobectomy for a mass lesion. The histology revealed dual pathology of anaplastic oligodendroglioma and B cell non-Hodgkin lymphoma. Postoperatively, the patient received whole brain radiotherapy. The patient remained well after 18 months of follow-up with no radiological progression of a known tumor residuum.

Brain Neoplasms↗
PubMedDate not supplied

Biochemical evidence for mediatory role of 5-hydroxytryptamine in the uterotonic action of prostaglandin F2oc.

5-Hydroxytryptamine (5-HT) is reported to be involved in endogenous prostaglandin (PG)--modulated as well as exogenous PG-induced pharmacological activities including oxytocic effect of PGE1 PGE2oc Biochemical parameters were undertaken for further studies into the possible role of 5-HT in the uterotonic effect of PGF2oc on isolated oestronised rat uterus. The results substantiate the involvement of endogenous 5-HT in the uterotonic effect of PGF2oc.

Animals↗