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Biomedical subjects

A Ghosh

Publications and source records attributed to A Ghosh.

At least 199 records · Page 11Linked to original sources
PubMed1996

Evidence of a laminin binding protein on the surface of Leishmania donovani.

Both the promastigote and amastigote forms of the intracellular parasite, Leishmania donovani bind the basement membrane glycoprotein laminin with high affinity (Kd = 3.56 x 10(-9) M and 3.98 x 10(-9) M respectively) with approximately 9000 and approximately 800 sites per cell. Bound laminin was identified by direct autoradiography and the binding protein through analysis of the parasite extract by SDS-PAGE and immunoblotting. A major component of 67 kDa was detected. The same protein was obtained when parasite outer membrane proteins were adsorbed to laminin-sepharose affinity matrix and subsequently eluted with SDS. The binding affinity of the isolated receptor was similar to that of the whole cells. Such a receptor isolated in Leishmania for the first time, may function as one of the bridging molecules for extracellular matrix recognition.

Animals↗
PubMed1996

Characterization of sheep lacrimal-gland peroxidase and its major physiological electron donor.

A soluble sheep lacrimal-gland peroxidase was purified to apparent homogeneity. It had a native molecular mass of 75 kDa with a subunit molecular mass of 82 kDa and an isoelectric point of 6.5. Western blotting showed that it shares some of the enzyme antigenic determinants in common with other soluble peroxidases. The enzyme exhibits a Soret peak at 410 nm which is shifted to 431 nm by 5 equiv. of H2O2 due to the formation of compound II. The latter is, however, unstable and gradually returns to the native state. The enzyme forms complexes with CN- and N3- and is reduced by dithionite showing a characteristic reduced peroxidase spectrum. Although the enzyme oxidizes I-, SCN- and Br- optimally at pH 5.5., 5.25 and 5.0 respectively, at physiological pH, it oxidizes I- and SCN- only. Since extracellular SCN- concentration is much higher than I-, SCN- may act as the major electron donor to the enzyme. The second-order rate constants for the reaction of the enzyme with H2O2 (k+1) and of compound I with SCN- (k+2) were 4 X 10(7) M-1 X s-1 and 8.1 X 10(5) M-1 X s-1 respectively. A plot of log Vmax against pH yields a sigmoidal curve consistent with a single ionizable group on the enzyme with a pK(a) value of 5.75, controlling thiocyanate oxidation. In a coupled system with the peroxidase, H2O2, SCN-, GSH, NADPH and glutathione reductase, peroxidase-catalysed SCN- oxidation by H2O2 could be coupled to NADPH consumption. The system is proposed to operate in vivo for the efficient elimination of endogenous H2O2.

Animals↗
PubMed1996

Cortical development: with an eye on neurotrophins.

Recent observations suggest that neurotrophins are involved in activity-dependent plasticity of the developing cerebral cortex. What molecular mechanisms underlie activity-dependent competition between axons for trophic factors?

Animals↗
PubMed1996

Inhibition of replication of rinderpest virus by 5-fluorouracil.

5-Fluorouracil (5FU), an analogue of uracil, was found to inhibit the production of infectious particles of rinderpest virus (RPV) in Vero cells (African green monkey kidney cells) by 99%, at a concentration of 1 microgram/ml. The levels of individual mRNA specific for five of the virus genes were also reduced drastically, while the level of mRNA for a cellular housekeeping gene-glyceraldehyde-3-phosphate dehydrogenase (GAPDH)-was unaltered by fluorouracil treatment of infected cells. Both virus RNA and protein synthesis showed inhibition in a dose-dependent manner. The virions which budded out of 5-fluorouracil-treated cells also contained reduced amounts of virus proteins compared with virus particles from untreated cells.

Animals↗
PubMed1996

Synthesis of leader RNA and editing of P mRNA during transcription by rinderpest virus.

Purified rinderpest virus was earlier shown to transcribe in vitro, all virus-specific mRNAs with the promoter-proximal N mRNA being the most abundant. Presently, this transcription system has been shown to synthesize full length monocistronic mRNAs comparable to those made in infected cells. Small quantities of bi- and tricistronic mRNAs are also synthesized. Rinderpest virus synthesizes in vitro, a leader RNA of approximately 55 nucleotides in length. Purified rinderpest virus also exhibits RNA editing activity during the synthesis of P mRNA as shown by primer extension analysis of the mRNA products.

Animals↗
PubMed1996

Iron transport-mediated drug delivery using mixed-ligand siderophore-beta-lactam conjugates.

BACKGROUND: Assimilation of iron is essential for microbial growth. Most microbes synthesize and excrete low molecular weight iron chelators called siderophores to sequester and deliver iron by active transport processes. Specific outer membrane proteins recognize, bind and initiate transport of species-selective ferric siderophore complexes. Organisms most often have specific receptors for multiple types of siderophores, presumably to ensure adequate acquisition of the iron that is essential for their growth. Conjugation of drugs to synthetic hydroxamate or catechol siderophore components can facilitate active iron-transport-mediated drug delivery. While resistance to the siderophore-drug conjugates frequently occurs by selection of mutants deficient in the corresponding siderophore-selective outer membrane receptor, the mutants are less able to survive under iron-deficient conditions and in vivo. We anticipated that synthesis of mixed ligand siderophore-drug conjugates would allow active drug delivery by multiple iron receptor recognition and transport processes, further reducing the likelihood that resistant mutants would be viable. RESULTS: Mixed ligand siderophore-drug conjugates were synthesized by combining hydroxamate and catechol components in a single compound that could chelate iron, and that also contained a covalent linkage to carbacephalosporins, as representative drugs. The new conjugates appear to be assimilated by multiple active iron-transport processes both in wild type microbes and in selected mutants that are deficient in some outer membrane iron-transport receptors. CONCLUSIONS: The concept of active iron-transport-mediated drug delivery can now be extended to drug conjugates that can enter the cell through multiple outer membrane receptors. Mutants that are resistant to such conjugates should be severely impaired in iron uptake, and therefore particularly prone to iron starvation.

Anti-Bacterial Agents↗
PubMed1996

Species selectivity of new siderophore-drug conjugates that use specific iron uptake for entry into bacteria.

Siderophores selectively bind ferric iron and are involved in receptor-specific iron transport into bacteria. Several types of siderophores were synthesized, and growth-promoting or inhibitory activities when they were conjugated to carbacephalosporin, erythromycylamine, or nalidixic acid were investigated. Overall, 11 types of siderophores and 21 drug conjugates were tested against seven different bacterial species: Escherichia coli, Bordetella bronchiseptica, Pasteurella multocida, Pasteurella haemolytica, Streptococcus suis, Staphylococcus aureus, and Staphylococcus epidermidis. In some species, the inhibitory activities of the drug conjugates were associated with the ability of the bacteria to use the siderophore portion of the molecules for growth promotion in disc diffusion tests (0.04 mumol of conjugate or siderophore per disc). E. coli used catechol-based siderophore portions as well as hydroxamate-based tri-delta-OH-N-OH-delta-N-acetyl-L-ornithine ferric iron ligands for growth under iron-restricted conditions achieved by supplemental ethylenediamine di (O-hydroxyphenylacetic acid) (100 micrograms/ml) and was sensitive to carbacephalosporin conjugated to these siderophore types (up to a 34-mm-diameter inhibition zone). B. bronchiseptica used desferrioxamine B and an isocyanurate-based or trihydroxamate in addition to catechol-based siderophore portions for promotion but was not inhibited by beta-lactam conjugates partly because of the presence of beta-lactamase. P. multocida and P. haemolytica did not use any of the synthetic siderophores for growth promotion, and the inhibitory activities of some conjugates seemed partly linked to their ability to withhold iron from these bacteria, since individual siderophore portions showed some antibacterial effects. Individual siderophores did not promote S. suis growth in restrictive conditions, but the type of ferric iron ligands attached to beta-lactams affected inhibitory activities. The antibacterial activities of the intracellular-acting agents erythromycylamine and nalidixic acid were reduced or lost, even against S. aureus and S. epidermidis, when the agents were conjugated to siderophores. Conjugate-resistant E. coli mutants showed the absence of some iron-regulated outer membrane proteins in gel electrophoresis profiles and in specific phage or colicin sensitivity tests, implying that the drugs used outer membrane receptors of ferric complexes to get into cells.

Animals↗
PubMed1996

Strategies for production of a potential candidate vaccine for cholera.

First attempt at cholera vaccination was made by Jaime Ferran in 1884. Since then, a variety of strategies and methods have been evolved to create a safe, efficacious vaccine against cholera. For the first few years emphasis was on the development of parenteral vaccines. However, as a result of accumulation of a tremendous amount of knowledge, not only on Vibrio cholerae-the causative agent, but also on its interaction with the host, emphasis has shifted towards the development of oral vaccines. Two such vaccines, one killed, a whole cell/B subunit combination vaccine and the other a live attenuated one, have shown promise. The combination vaccine in its present state of development confers only a transient protection in young children, while the live attenuated one produces adverse reaction. To combat these, various strategies are being evolved. In one attempt, a potential candidate vaccine strain has been constructed from a non-reactogenic clinical isolate of V. cholerae, which is devoid of all known major virulence genes and is also a good colonizer. In animal studies this construct has shown considerable promise. This review discusses the various strategies that have been employed so far in the quest for an ideal cholera vaccine.

Administration, Oral↗
PubMed1996

Smoking habits and respiratory symptoms: observations among college students and professionals.

The study comprising smoking habits among educationally and socially forward class, its impact on respiratory system and response of the said class of people to a questionnaire was undertaken among a random sample of 1188 subjects consisting of students and professionals aged between 15 and 65 years. Results showed that smoking habit was alarmingly high (48.8%) among the students and a little higher (53%) among the professionals. The exact nature and extent of the problem of smoking was not very much clear to all the subjects.

Adolescent↗
PubMed1996

Antifungal susceptibility pattern of non-albicans Candida species & distribution of species isolated from Candidaemia cases over a 5 year period.

A marked increase in the incidence of patients of candidaemia is reported from a tertiary care hospital in north India over the last five years (15 patients in 1991 and 275 in 1995). The distribution of Candida species isolated from January 1991 through December 1995 was investigated. Antifungal susceptibility against amphotericin B, 5-fluorocytosine, ketoconazole and fluconazole of 100 randomly selected non-albicans Candida species isolated during 1995 was determined by an in-house standardized disc diffusion method and the standard broth dilution procedure recommended by the National Committee for Clinical Laboratory Standards (NCCLS, USA). The disc diffusion method correlated well with NCCLS method except for ketoconazole. Resistance against any antifungal was confirmed only by results of NCCLS method. A shift to higher isolation of non-albicans Candida species was observed during this period (52.6% in 1992 to 89.5% in 1995). Resistance was observed against 5-fluorocytosine in 3 per cent strains of C. krusei; and against fluconazole in 24.2 per cent of C. krusei, 15.4 per cent of C. guilliermondii and 5.7 per cent strains of C. tropicalis. No resistance was detected against amphotericin B and ketoconazole. Thus Candida species with fluconazole resistance have become more prominent in recent years.

Antifungal Agents↗
PubMed1996

In vivo effect of chemically induced fibrosarcoma on copper metabolism of liver in mice.

Copper and ceruloplasmin concentrations were determined in different subcellular fractions of liver of mice bearing benzo(a)pyrene induced fibrosarcoma. Though the copper content was elevated in the nuclear, mitochondrial and lysosomal fractions of tumor bearing mice, the microsomal and soluble supernatant fractions showed a downward trend in their copper concentration when compared to the controls. Similarly, ceruloplasmin concentration in the different subcellular fractions also showed variable results. This study was aimed to ascertain the distribution of copper. The incorporation of radioactive copper in different fractions was also monitored. The possible reasons for the variation in copper and ceruloplasmin concentrations observed during malignancy in the tumor bearing animals, has been discussed.

Animals↗
PubMed1995

Characterization of phage phi O139, a Vibrio cholerae O139 temperate bacteriophage with cohesive DNA termini.

A temperate bacteriophage isolated from Vibrio cholerae O139, the new epidemic strain of cholera, was found to have a polyhedral head 65 nm in diameter and a rigid contractile tail 120 nm in length. The phage chromosome was a double-stranded DNA of 35 kb, with unique cohesive ends and had a G + C content of 58.8%. A restriction map of the phage DNA was constructed using the restriction endonucleases AvaI and BstEII. The phage, whose presence could be detected in nine out of 13 V. cholerae O139 isolates tested, was found to have identical chromosomal integration sites in all the strains. The phage attachment site (attP) was found to be located very close to one end of the genome.

Bacteriophages↗
PubMed1995

Calcium activation of Ras mediated by neuronal exchange factor Ras-GRF.

Tyrosine kinase receptors stimulate the Ras signalling pathway by enhancing the activity of the SOS nucleotide-exchange factor. This occurs, at least in part, by the recruitment of an SOS-GRB2 complex to Ras in the plasma membrane. Here we describe a different signalling pathway to Ras that involves activation of the Ras-GRF exchange factor in response to Ca2+ influx. In particular, we show that the ability of Ras-GRF to activate Ras in vivo is markedly enhanced by raised Ca2+ concentrations. Activation is mediated by calmodulin binding to an IQ motif in Ras-GRF, because substitutions in conserved amino acids in this motif prevent both calmodulin binding to Ras-GRF and Ras-GRF activation in vivo. So far, full-length Ras-GRF has been detected only in brain neurons. Our findings implicate Ras-GRF in the regulation of neuronal functions that are influenced by Ca2+ signals.

Amino Acid Sequence↗
PubMed1995

Calcium signaling in neurons: molecular mechanisms and cellular consequences.

Neuronal activity can lead to marked increases in the concentration of cytosolic calcium, which then functions as a second messenger that mediates a wide range of cellular responses. Calcium binds to calmodulin and stimulates the activity of a variety of enzymes, including calcium-calmodulin kinases and calcium-sensitive adenylate cyclases. These enzymes transduce the calcium signal and effect short-term biological responses, such as the modification of synaptic proteins and long-lasting neuronal responses that require changes in gene expression. Recent studies of calcium signal-transduction mechanisms have revealed that, depending on the route of entry into a neuron, calcium differentially affects processes that are central to the development and plasticity of the nervous system, including activity-dependent cell survival, modulation of synaptic strength, and calcium-mediated cell death.

Animals↗
PubMed1995

A mutation in the Schizosaccharomyces pombe rae1 gene causes defects in poly(A)+ RNA export and in the cytoskeleton.

A collection of fission yeast Schizosaccharomyces pombe conditional mutants was screened for defective nucleocytoplasmic transport of poly(A)+ RNA by fluorescence in situ hybridization. We identified a temperature-sensitive mutant that accumulated poly(A)+ RNA in the nucleus and have named it rae1-1, for ribonucleic acid export. All rae1-1 cells exhibit the defect in poly(A)+ RNA export within 30 min following a shift to the non-permissive temperature. In addition, in the rae1-1 mutant, actin and tubulin become disorganized, and cells undergo an irreversible cycle arrest. Results from experiments in which rae1-1 cells were arrested in various phases of the cell division cycle and then shifted to nonpermissive temperature suggest that cells are particularly vulnerable to loss of rae1 function during G2/M. However, the inability to export RNA from the nucleus to the cytoplasm was not limited to a particular phase of the cell division cycle. The rae1 gene was isolated by complementation and encodes a predicted protein of 352 amino acids with four beta-transducin/WD40 repeats.

Actins↗