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D Das

Publications and source records attributed to D Das.

At least 19 recordsLinked to original sources
PubMed2001

Weak and strong dynamic scaling in a one-dimensional driven coupled-field model: effects of kinematic waves.

We study the coupled dynamics of the displacement fields in a one-dimensional coupled-field model for drifting crystals, first proposed by Lahiri and Ramaswamy [Phys. Rev. Lett. 79, 1150 (1997)]. We present some exact results for the steady state and the current in the lattice version of the model for a special subspace in the parameter space, within the region where the model displays kinematic waves. We use these results to construct the effective continuum equations corresponding to the lattice model. These equations decouple at the linear level in terms of the eigenmodes. We examine the long-time, large-distance properties of the correlation functions of the eigenmodes by using symmetry arguments, Monte Carlo simulations, and self-consistent mode-coupling methods. For most parameter values, the scaling exponents of the Kardar-Parisi-Zhang equation are obtained. However, for certain symmetry-determined values of the coupling constants the two eigenmodes, although nonlinearly coupled, are characterized by two distinct dynamic exponents. We discuss the possible application of the dynamic renormalization group in this context.

Journal Article↗
PubMed2001

The binding interaction of HMG-1 with the TATA-binding protein/TATA complex.

High mobility protein-1 (HMG-1) has been shown to regulate transcription by RNA polymerase II. In the context that it acts as a transcriptional repressor, it binds to the TATA-binding protein (TBP) to form the HMG-1/TBP/TATA complex, which is proposed to inhibit the assembly of the preinitiation complex. By using electrophoretic mobility shift assays, we show that the acidic C-terminal domain of HMG-1 and the N terminus of human TBP are the domains that are essential for the formation of a stable HMG-1/TBP/TATA complex. HMG-1 binding increases the affinity of TBP for the TATA element by 20-fold, which is reflected in a significant stimulation of the rate of TBP binding, with little effect on the dissociation rate constant. In support of the binding target of HMG-1 being the N terminus of hTBP, the N-terminal polypeptide of human TBP competes with and inhibits HMG-1/TBP/TATA complex formation. Deletion of segments of the N terminus of human TBP was used to map the region(s) where HMG-1 binds. These findings indicate that interaction of HMG-1 with the Q-tract (amino acids 55-95) in hTBP is primarily responsible for stable complex formation. In addition, HMG-1 and the monoclonal antibody, 1C2, specific to the Q-tract, compete for the same site. Furthermore, calf thymus HMG-1 forms a stable complex with the TBP/TATA complex that contains TBP from either human or Drosophila but not yeast. This is again consistent with the importance of the Q-tract for this stable interaction and shows that the interaction extends over many species but does not include yeast TBP.

Amino Acid Sequence↗
PubMed2001

Mathematical model for evaluation of mass transfer limitations in phenol biodegradation by immobilized Pseudomonas putida.

A mathematical model is proposed to analyze the mass transfer limitations in phenol biodegradation using Pseudomonas putida immobilized in calcium alginate. The model takes into account internal and external mass transfer limitations, substrate inhibition kinetics and the dependence of the effective diffusivity of phenol in alginate gel on cell concentration. The model is validated with the experimental data from batch fermentation. The effect of various operating conditions such as initial phenol concentration, initial cell loading, alginate gel loading on the biodegradation of phenol is experimentally demonstrated. Phenol degradation time is found to decrease initially and reach stationary value with increase in cell loading as well as gel loading. The model predicts these trends reasonably well and shows the presence of external mass transfer limitations. A new concept of effectiveness factor is introduced to analyze the overall performance of batch fermentation.

Biodegradation, Environmental↗
PubMed2001

A novel method for eliminating the melanin pigments from melanoma cells undergoing cytogenetic analysis in cases of uveal melanoma.

A method has been developed to eliminate melanin pigments from chromosomal plates of uveal melanoma tumors. On preparing the chromosomal plates of tumor masses of posterior uveal melanoma for cytogenetic analysis in intermediate pigmented population, it was found that the melanin pigments obscured the cells and thereby the chromosomes. Thus, cytogenetic analysis could not be carried out. Hence, a method was developed in our laboratory to eliminate these obscuring pigments. Several different attempts were made to eliminate the melanin pigments. Finally, washing the cells with phosphate buffered saline before the harvesting stage served the purpose. After harvesting and preparing the chromosomal plates, the cells were found to be devoid of melanin pigments. The protocol would help researchers trying to carry out cytogenetic analysis on melanoma tumor masses in populations with intermediate to dark pigmentation.

Cytogenetics↗
PubMed2000

Antioxidant properties of colchicine in acute carbon tetrachloride induced rat liver injury and its role in the resolution of established cirrhosis.

Antioxidant and antifibrotic properties of colchicine were investigated in the carbon tetrachloride (CCl(4)) rat model. (1) The protective effect of colchicine pretreatment on CCl(4) induced oxidant stress was examined in rats subsequently receiving a single lethal dose of CCl(4). Urinary 8-isoprostane, kidney and liver malondialdehyde and kidney glutathione levels increased following CCl(4) treatment, but only the rise in kidney malondialdehyde was significantly inhibited by colchicine pretreatment. Serum total antioxidant levels were significantly higher in the colchicine pretreatment group. (2) The long term effects of colchicine treatment on CCl(4) induced liver damage were investigated using liver histology and biochemical markers (hydroxyproline and type III procollagen peptide). Co-administration of colchicine with sub-lethal doses of CCl(4) over 10 weeks did not prevent progression to cirrhosis. However, rats made cirrhotic with repeated CCl(4) challenge and subsequently treated with colchicine for 12 months, all showed histological regression of cirrhosis. (3) The antioxidant effect of colchicine in vitro was evident only at very high concentrations compared to other plasma antioxidants. In summary, colchicine has only weak antioxidant properties, but does afford some protection against oxidative stress; more importantly, long term treatment with this drug may be of value in producing regression of established cirrhosis.

Animals↗
PubMed2000

Particles sliding on a fluctuating surface: phase separation and power laws

We study a system of hard-core particles sliding locally downwards on a fluctuating one-dimensional surface characterized by a dynamical exponent z and no overall tilt. In numerical simulations, an initially random particle density is found to coarsen and obey scaling with a growing length scale approximately t(1/z). The structure factor deviates from the Porod law for the models studied. The steady state is unusual in that the density-segregation order parameter shows strong fluctuations. The two-point correlation function has a scaling form with a cusp at small argument which we relate to a power law distribution of particle cluster sizes. Exact results on a related model of surface depths provide insight into this behavior.

Journal Article↗
PubMed2000

MAPK-dependent expression of p21(WAF) and p27(kip1) in PMA-induced differentiation of HL60 cells.

Treatment of HL60 cells with phorbol 12-myristate 13-acetate (PMA) results in growth arrest and differentiation towards the macrophage lineage. PMA-induced changes are easily monitored by morphological changes while cells in suspension start adhering onto substrate. PMA induces rapid activation of the extracellular signal-regulated kinases (ERKs). Activation of the ERK pathway is essential to PMA-induced differentiation of HL60 cells. PMA also induces the expression of the cyclin-dependent kinase inhibitors p21(WAF) and p27(kip1), which is modulated by the use of an inhibitor of the ERK cascade. This implies that a link exists between ERK activation and p21(WAF) and p27(kip1) induction in the process of terminal differentiation.

Cell Cycle Proteins↗
PubMed2000

Evidence for digenic inheritance in some cases of Antley-Bixler syndrome?

The Antley-Bixler syndrome has been thought to be caused by an autosomal recessive gene. However, patients with this phenotype have been reported with a new dominant mutation at the FGFR2 locus as well as in the offspring of mothers taking the antifungal agent fluconazole during early pregnancy. In addition to the craniosynostosis and joint ankylosis which are the clinical hallmarks of the condition, many patients, especially females, have genital abnormalities. We now report abnormalities of steroid biogenesis in seven of 16 patients with an Antley-Bixler phenotype. Additionally, we identify FGFR2 mutations in seven of these 16 patients, including one patient with abnormal steroidogenesis. These findings, suggesting that some cases of Antley-Bixler syndrome are the outcome of two distinct genetic events, allow a hypothesis to be formulated under which we may explain all the differing and seemingly contradictory circumstances in which the Antley-Bixler phenotype has been recognised.

Abnormalities, Drug-Induced↗
PubMed2000

Prevalence of hepatitis B infection among the primitive tribes of Andaman & Nicobar Islands.

BACKGROUND & OBJECTIVES: Andaman and Nicobar Islands, is the home of six primitive tribes. No information is available on the prevalence of hepatitis B virus (HBV) infection among them. Hence a study was undertaken with the objective of assessing the sero-prevalence of HBV infection among the four accessible tribes of these islands. METHODS: A total of 1266 serum samples were collected from four tribes i.e., Nicobarese, Shompens, Onges and Great Andamanese and tested for the presence of HBsAg and anti-HBs. Information about different risk factors associated with HBV infection was also collected from the Nicobarese tribe. RESULTS: The overall seropositivity rate of HBsAg among the Nicobarese was 23.3 per cent (95% C.I. 21.0-25.9). Hepatitis B was also found to be an important health problem among the Shompens and Onges with HBsAg positivity of 37.8 and 31.0 per cent respectively. The age-wise distribution of these serological markers among Nicobarese tribe indicate that the infection is very common in all the age groups. The sero-prevalence was also found to be very high among the children. CONCLUSIONS & INTERPRETATION: The findings of the present study indicate that hepatitis B infection is hyper endemic among the primitive tribes of these islands. Though none of the risk factors studied in the Nicobarese was found to be significantly associated with HBV infection, the fact that almost 20 per cent of the women in the reproductive age group were positive for HBsAg indicates the possibility of vertical transmission among the Nicobarese. Further studies are required to find out other modes of transmission.

Adolescent↗
PubMed1999

Solid matrix characterization of immobilized Pseudomonas putida MTCC 1194 used for phenol degradation.

Characterization studies of calcium alginate beads with encapsulated Pseudomonas putida MTCC 1194, used for the biodegradation of phenol, were carried out to investigate the reactivity, reusability and structural strength of the solid matrix. Various techniques were employed to improve the structural stability of the immobilized solid necessary for its use in commercial reactors like packed bed flow reactor, fluidized bed and CSTR systems. Experiments were performed to establish the optimum conditions for durability, strength and steady biochemical reactivity. During a batch run of 40 h a gradual decline in the rate of phenol degradation was observed with the immobilized system. The calcium alginate beads with high structural strength yielded decreased activity. Treatment with a hardening agent like glutaraldehyde for different concentrations and treatment times led to variations in structural stability, reusability and the extent of phenol degradation. Scanning electron microscope studies of the immobilized solid indicated the internal distribution pattern of the cells encapsulated in a calcium alginate bead.

Alginates↗
PubMed1999

Visual pigments and oil droplets in the retina of a passerine bird, the canary Serinus canaria: microspectrophotometry and opsin sequences.

The visual receptors of the passeriform bird Serinus canaria, the canary, have been examined microspectrophotometrically and the sequences of the opsins determined. Rods have a maximum absorbance (lambda max) at 506 nm. Four spectral classes of single cone are present: long-wave-sensitive (LWS) containing a photopigment with lambda max at 569 nm, middle-wave-sensitive (MWS) with lambda max at 505 nm, short-wave-sensitive (SWS) with lambda max at 442 nm, and ultraviolet-sensitive (UVS) with lambda max at about 366 nm. Double cones possess the 569-nm pigment in both members. Typical combinations of photopigment and oil droplet occur in most cone classes. An ambiguity exists in the oil droplet of the single LWS cones. In some birds, LWS cones are paired with an R-type droplet, whereas in the majority of canaries the LWS pigment is paired with a droplet similar to the P-type of double cones. Mechanisms of spectral tuning within each opsin class are discussed.

Animals↗
PubMed1999

Hepatic sarcoidosis and renal carcinoma.

Sarcoidosis is a relatively common, chronic, multisystem disease of unknown origin. It most commonly affects young adults and usually manifests with bilateral hilar lymphadenopathy or pulmonary infiltrates. Alternatively, it may present with protean manifestations. It has been documented in all organs of the body, with the exception of the adrenal gland. We describe a male patient who presented with hepatic sarcoidosis, with a sclerosing cholangitis-like picture, but without any pulmonary involvement. He was treated with prednisolone and cyclophosphamide, the latter as a steroid-sparing agent. A few years later, renal adenocarcinoma developed. We postulate that this could be related to cyclophosphamide treatment. We present this case history for two reasons: (1) sarcoidosis, selectively affecting the liver and lymph nodes but not the lung, with its hepatic involvement mimicking sclerosing cholangitis, has not previously been reported: and (2) although long-term cyclophosphamide treatment is known to be associated with malignancy, there is only one previous report of its association with a renal adenocarcinoma.

Carcinoma, Renal Cell↗
PubMed1999

Hypertensive encephalopathy in a patient with retroperitoneal fibrosis.

A patient presented with retroperitoneal fibrosis but without any ureteric obstruction. The diagnosis was made by an abdominal CT scan and also at laparotomy. Post-operatively, she developed hypertensive encephalopathy. An isotope renogram with captopril was abnormal but not diagnostic of renal artery stenosis. The patient's condition improved with steroid and antihypertensive treatment. A follow-up CT scan showed complete resolution of peri-aortic thickening. A causative link is postulated between retroperitoneal fibrosis, trauma during laparotomy, and onset of acute hypertension.

Anti-Inflammatory Agents↗
PubMed1998

The molecular basis for UV vision in birds: spectral characteristics, cDNA sequence and retinal localization of the UV-sensitive visual pigment of the budgerigar (Melopsittacus undulatus).

Microspectrophotometric (msp) studies have shown that the colour-vision system of many bird species is based on four pigments with absorption peaks in the red, green, blue and UV regions of the spectrum. The existence of a fourth pigment (UV) is the major difference between the trichromacy of humans and the tetrachromacy of such birds, and recent studies have shown that it may play a determining role in such diverse aspects of behaviour as mate selection and detection of food. Avian visual pigments are composed of an opsin protein covalently bound via a Schiff-base linkage to the chromophore 11-cis-retinal. Here we report the cDNA sequence of a UV opsin isolated from an avian species, Melopsittacus undulatus (budgerigar or small parakeet). This sequence has been expressed using the recombinant baculovirus system; the pigment generated from the expressed protein on addition of 11-cis-retinal yielded an absorption spectrum typical of a UV photopigment, with lambdamax 365+/-3 nm. This is the first UV opsin from an avian species to be sequenced and expressed in a heterologous system. In situ hybridization of this sequence to budgerigar retinas selectively labelled a sub-set of UV cones, representing approx. 9% of the total cone population, that are distributed in a semi-regular pattern across the entire retina.

Amino Acid Sequence↗
PubMed1998

Oxidative inactivation of gastric peroxidase by site-specific generation of hydroxyl radical and its role in stress-induced gastric ulceration.

We have shown earlier that restraint-cold stress-induced gastric ulceration in rats is caused by metal ion-dependent generation of hydroxyl radical (OH.) and oxidative inactivation of the gastric peroxidase (GPO), an important H2O2 scavenging enzyme. To study the mechanism of the oxidative damage of GPO, the purified enzyme was exposed to an OH. generating system containing Cu2+, ascorbate, and H2O2. Kinetic studies indicate that the enzyme is inactivated in a time-dependent process showing saturation with respect to Cu2+ concentration. The enzyme specifically requires Cu2+ and is not inactivated by the same concentration of Fe2+, Mn2+, or Zn2+. Sensitivity to catalase indicates the critical role of H2O2 in the inactivation. Inactivation is insensitive to superoxide dismutase, suggesting no role of superoxide. The rate of inactivation is not increased in D2O excluding the involvement of singlet oxygen in the process. However, OH. scavengers such as benzoate or mannitol cannot prevent inactivation. The results indicate a plausible generation of OH. within the enzyme molecule as the cause of inactivation. Fragmentation of peptide linkage or intramolecular crosslinking, gross change of tertiary structure, or change in intrinsic tryptophan fluorescence which occurs in "global" oxidation are not evident. Inactivation is dependent on pH and from a plot of K(obs) of inactivation against pH, the controlling role of an ionizable group of the enzyme having a pka of 7.8 could be suggested, deprotonation of which favors inactivation. Amino acid analysis shows a specific loss of two lysine residues in the inactivated enzyme. Competitive kinetic studies indicate that pyridoxal phosphate, a specific modifier of the lysine residue, prevents inactivation by competing with Cu2+ for binding at the GPO. A Cu2+ binding motif consisting at least of two lysine residues exists in GPO, which specifically binds Cu2+ and generates OH.. The radical oxidizes the lysine residues and perturbs the heme environment to cause inactivation. We suggest that oxidative damage of GPO is mediated by site-specific generation of OH. and not by the OH. generated in the bulk phase.

Animals↗
PubMed1998

Setaria digitata adult 14- to 20-kDa antigens induce differential Th1/Th2 cytokine responses in the lymphocytes of endemic normals and asymptomatic microfilariae carriers in bancroftian filariasis.

High titers of parasite antigen-specific IgG4 antibodies have been found to be circulating in the peripheral blood of chronic patients, asymptomatic microfilariae carriers, and endemic normals in bancroftian filariasis. But in contrast to this, the titers of antigen-specific IgG1, IgG2, and IgG3 isotype antibodies are much lower. Using soluble antigens of adult Setaria digitata, a cattle parasite which shows strong antigenic reactivity with filaria sera, we have identified, by immunoblot, 14- to 20-kDa antigens which are recognized only by the IgG4 isotype antibodies present in the sera of asymptomatic microfilariae carriers. These 14- to 20-kDa antigens, after fractionation by SDS-PAGE and transfer to nitrocellulose paper, when solubilized and tested in vitro, induced secretion of a higher quantity of IFN-gamma and a lower quantity of IL-4, IL-5, and IL-10 (differential Th1 and Th2 response) in the lymphocytes of endemic normals in comparison to what they induced in the lymphocytes of asymptomatic microfilariae carriers.

Adolescent↗
PubMed1998

Management of glass intraocular foreign bodies.

PURPOSE: To describe the results of management of glass intraocular foreign bodies (IOFBs). METHODS: A total of 51 eyes of 43 patients that sustained penetrating injury with glass IOFB were studied retrospectively. A total of 23.5% had IOFB only in the anterior segment; the rest had IOFB in the posterior segment alone or in both the anterior and posterior segments. Six eyes were followed conservatively despite IOFB in a functional eye. Removal of IOFB was combined with repair of retinal detachment (where present) using internal tamponade with gas or silicone oil or buckle. RESULTS: After a mean follow-up of 16.8 months, 66.7% of eyes recovered better than 6/60 (20/200) vision and 75.6% had attached retina. On univariate analysis, scleral entry wound, posterior segment IOFB, larger size of IOFB, and retinal damage were found to be associated with poor anatomic outcome. Lower presenting visual acuity, hyphema, retinal damage, subretinal hemorrhage, detached retina, and larger IOFB were associated with a poor functional result. Multivariate analysis identified retinal damage caused by the foreign body as the only factor significantly associated with poor anatomic as well as functional outcome. CONCLUSIONS: Glass IOFBs are caused in a majority of cases by blast injury. Bilaterality is not uncommon. Presence of retinal damage is predictive of poor functional and anatomic results. Overall results are modest with modern vitreoretinal surgical techniques.

Adult↗