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Biomedical subjects

D Das

Publications and source records attributed to D Das.

At least 37 records · Page 2Linked to original sources
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↗
PubMed1998

Cognitive decline in patients on an acute geropsychiatric unit.

The authors compared patients in a geropsychiatric unit who showed marked cognitive decline during hospitalization with those who did not. Patients who declined in cognitive function were older, were more likely to have a diagnosis of dementia, and were more anergic on admission. These patients were also discharged to more restrictive living environments. The subgroup of demented patients who declined in cognitive function were also older and improved less on anxiety and depression.

Age Factors↗
PubMed1997

Biochemical and immunological characterization of soluble antigens of Giardia lamblia.

The crude soluble antigens (CSA) of Giardia lamblia trophozoites and their analytically purified fractions were characterized biochemically and immunologically to determine the most immunogenic fraction and its localization on the parasite. Both Sephacryl S-300 column chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) revealed the highly complex and heterogeneous nature of CSA. Gel filtration of CSA showed four fractions (FI-FIV) with molecular masses of 250, 150, 110, and 10 kDa for fractions I-IV, respectively. Protein profiles of CSA demonstrated 28 Coomassie-blue bands in the range of 200-14 kDa. Similar banding patterns with fewer polypeptides were observed in the FI fraction. However, fractions II and III showed polypeptide bands in the region of 97-14 kDa. The glycoprotein nature of CSA and its-fractions were demonstrated in physicochemical analysis. In antigenic activity analysis the high-molecular-weight FI antigen was found to be 8 times more immunogenic than CSA as well as the other fractions. Major differences in the immunoreactivity of CSA and FI antigens were noted at 220, 30, and 22 kDa for the FI antigen and at 205, 84, 55, 43, and 20 kDa for CSA. Some of these FI polypeptides were found to be surface-associated as revealed by immunofluorescence and immunoblot assay. These results suggest the future use of the FI antigen in the serodiagnosis of and immunoprophylaxis against giardiasis.

Animals↗
PubMed1997

Hydroxyl radical is the major causative factor in stress-induced gastric ulceration.

The role of the metal-catalyzed production of hydroxyl radicals (OH.) on gastric ulceration caused by restraint-cold stress in rat was studied. Stress causes a 50% increase in the thiobarbituric acid reactive species (TBARS) as a measure of the lipid peroxidation, nearly 70% increase in protein oxidation as measured by its carbonyl content and about 40% decrease in the glutathione content of the fundic stomach, suggesting oxidative damage by stress. Stress also causes a time-dependent increase in the mitochondrial superoxide dismutase activity and a decrease in the peroxidase activity, both of which correlate well with the increase in the severity of ulceration as measured by the ulcer index. Specific OH. scavengers such as benzoate or dimethylsulfoxide (DMSO) and the free radical trap such as alpha-phenyl N-tert-butyl nitrone (PBN) significantly inhibit gastric ulceration suggesting the role of OH. in this oxidative damage. Desferrioxamine (DFO), a nontoxic transition metal ion chelator, protects the mucosa against stress-ulceration dose dependently. Increased level of TBARS and the inactivation of gastric peroxidase are also prevented by DFO or by antioxidants such as glutathione or vitamin E, suggesting the critical role of metal ion and OH. in the oxidative damage. A metal-catalyzed OH. generating system constituted by Cu2+, H2O2 and ascorbate (reducing equivalent of O2-) causes inactivation of the purified gastric peroxidase in vitro, which can be effectively prevented by DFO. The stress-induced activation of the superoxide dismutase is completely blocked by pretreatment with alpha-amanitin indicating an increased synthesis of the enzyme by increased transcription of its m-RNA. Quantitative measurement indicates that stress causes a fivefold increase in the generation of OH., which correlates well with the increase in ulcer index with the progress of stress. The results indicate that the stress-induced gastric ulceration is a consequence of the oxidative damage of the gastric mucosa. This is caused by the OH. generated through the metal-catalyzed Haber-Weiss reaction between O2- and H2O2, the latter being formed by the stimulation of the superoxide dismutase and inactivation of the gastric peroxidase.

Amanitins↗
PubMed1997

Specific binding of inorganic mercury to Na(+)-K(+)-ATPase in rat liver plasma membrane and signal transduction.

Specific binding of Hg2+ to ouabain-sensitive Na(+)-K(+)-ATPase of rat liver plasma membrane was demonstrated with a Ka of 2.64 x 10(9) and Bmax of 1.6 nmole mg-1 protein. The binding of mercury to the enzyme also causes significant inhibition of the enzyme, which is greater than its ouabain sensitivity. In the cytosol Hg2+ binding to reduced glutathione (GSH) is stimulated by GSH-S-transferase (GST), the activity of which was found to be significantly enhanced by 15 mM Na+ and 10 mM Hg2+. It is proposed that the transport of Hg2+ inside the cell takes place by increased dissociation of Hg2+ from the membrane due to greater avidity of Hg2+ towards cytosolar GSH binding. The GSH-Hg complex enters the nucleus where it dissociates to bind the metal response element (MRE) of the metallothionein (MT) gene to induce MT transcription.

Animals↗
PubMed1997

Role of exogenous reduced glutathione on time dependent 203Hg distribution in liver and kidney of a freshwater teleost, Anabas testudineus.

Time-dependent tissue distribution of mercury(Hg) was studied in a freshwater perch, Anabas testudineus which revealed that the liver and kidneys are the major sites of Hg retention. The role of reduced glutathione (GSH) in the clearance of Hg was also investigated to evaluate the ameliorative effect of this nucleophile. For this purpose, the perch was given GSH 15 min before or after they received 203Hg by injection. The fish were then sacrificed at 24 h and 48 h later. The results clearly indicate that exogenous GSH can significantly reduce Hg retention in both the liver and kidneys, demonstrating a direct role of this nucleophile in the amelioration of Hg-induced toxicity in the early phase of intoxication.

Animals↗
PubMed1996

Thermostable alpha-amylase production using Bacillus licheniformis NRRL B14368.

Maximum amount of extracellular alpha-amylase of B. licheniformis NRRL B14368 was obtained at the stationary phase. Highest yield of alpha-amylase was achieved with high level of crude protein and low carbohydrate level. There was a catabolite repression in the organism. Protease was produced concurrently with alpha-amylase. It was also observed that soyabean acts as an inhibitor of the protease. Optimum pH and temperature of alpha-amylase were 5-7 and 76 degrees C respectively. It was also observed that alpha-amylase production was a non-growth associated product. Maltose was an excellent inducer for alpha-amylase production. Ca2+ (0.01 M) increased the thermostability of the enzyme. Alpha-amylase purification studies were carried out by using isopropanol, acetone, ammonium sulphate solution, ion exchange chromatography. Acetone was found most suitable for the separation of alpha-amylase. Protein recovery and relative enzyme activity (as compared to that of the maximum activity of the crude enzyme) were 30.77% and 3.03 respectively.

Bacillus↗
PubMed1995

Thiocyanate, a plausible physiological electron donor of gastric peroxidase.

Gastric peroxidase (GPO) was purified to apparent homogeneity to characterize its major physiological electron donor. The enzyme (RZ = 0.7), with a subunit molecular mass of 50 kDa, is a glycoprotein, with a relative abundance of aspartic and glutamic acid over arginine and lysine. It has a Soret maximum at 412 nm, which is shifted to 426 nm by H2O2 due to formation of compound II. Although the physiological electron donors I-, Br- and SCN-, but not Cl-, are oxidized by GPO optimally at acid pH, only I- and SCN- are oxidized appreciably at physiological pH. Considering that the I- concentration in stomach is less than 1 microM, whereas the SCN- concentration is about 250 microM, SCN- may act as a major electron donor for GPO. Moreover, SCN- oxidation remains unaltered in the presence of physiological concentrations of other halides. The second-order rate constant for the reaction of GPO with H2O2 (k1) and compound I with SCN- (k2) at pH 7 was found to be 8 x 10(7) M-1.s-1 and 2 x 10(5) M-1.s-1 respectively. GPO has significant pseudocatalase activity also in the presence of I- or Br-, but it is blocked by SCN-. The SCN- oxidation product OSCN- may be reduced back to SCN- by cellular GSH, and GSSG may be reduced back to GSH by glutathione reductase and NADPH. In a system reconstituted with pure glutathione reductase, NADPH, GSH, SCN- and H2O2. GPO-catalysed SCN- oxidation could be coupled to NADPH oxidation. This system where GPO utilizes SCN- as the major physiological electron donor may operate efficiently to scavenge intracellular H2O2.

Animals↗