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A Chattopadhyay

Publications and source records attributed to A Chattopadhyay.

At least 19 recordsLinked to original sources
PubMed1995

Effect of glutathione on sister-chromatid exchanges in normal and buthionine sulfoximine-treated mice.

Based on their ability to induce sister-chromatid exchanges (SCEs) it is evident that thiol-containing radioprotectors can induce DNA damage. However, there were contradictory findings when reduced glutathione (GSH) was tested using two cell lines. The present study demonstrated that GSH can induce SCEs and also delay in cell proliferation in mouse bone marrow cells in vivo. The presence of catalase significantly reduced GSH-induced SCE frequency down to catalase alone levels. An attempt was made to evaluate the effect of GSH treatment in buthionine sulfoximine (BSO)-treated mice (GSH-depleted mice) and the data indicate that induction of SCEs takes place without inducing a delay in cell proliferation or the generation of hydrogen peroxide. Probably, some unknown route is involved by which GSH-degraded product(s) induce SCEs in BSO-treated mice. Therefore, the induction of SCEs by GSH in normal mice may be largely due to hydrogen peroxide generation; however, the involvement of the binding ability of GSH to chromatin and the probable (unknown) route by which GSH-degraded product(s) may cause smaller fraction of SCEs cannot be ruled out.

Animals↗
PubMed1994

Motionally restricted tryptophan environments at the peptide-lipid interface of gramicidin channels.

The tryptophans in the gramicidin channel play a crucial role in the organization and function of the channel. The localization and dynamics of these tryptophans have been studied using fluorescence spectroscopy, especially utilizing environment-induced effects on the rates of solvent relaxation around these residues in membranes. When incorporated into model membranes of dioleoyl-sn-glycero-3-phosphocholine (DOPC), the tryptophans in the gramicidin channel exhibit a red edge excitation shift (REES) of 6 nm. In addition, fluorescence polarization shows both excitation and emission wavelength dependence. Fluorescence lifetime analysis shows a biexponential decay, corresponding to a short- and a long-lifetime component. The mean lifetime was found to be dependent on both excitation and emission wavelengths. Analysis of time-resolved emission spectra (TRES) shows a heterogeneous environment for the tryptophans consistent with the lifetime information. Taken together, these observations point out the motional restriction experienced by the tryptophans in the gramicidin channel. This is consistent with other studies in which such restrictions are thought to be imposed due to hydrogen bonding between the indole rings of the tryptophans and the neighboring lipid carbonyls. The significance of such organization in terms of functioning of the channel is brought out by the fact that substitution, photodamage, or chemical modification of these tryptophans is known to give rise to channels with conformation and reduced conductivity.

Gramicidin↗
PubMed1994

Silver-binding nucleolar organizing regions: a study of oral leukoplakia and squamous cell carcinoma.

Silver-binding nucleolar organizing regions (AgNORs) in normal oral buccal mucosa epithelium, oral leukoplakia, and oral squamous cell carcinoma (SCC) were studied. The mean AgNOR count per nucleus increased from healthy mucosa to leukoplakia to SCC. Tissues showing dysplasia in leukoplakia and SCC cases showed higher counts, wider scatter, and smaller size of AgNOR dots in the nuclei. The study seems to suggest that this method has some potential in distinguishing between dysplastic and nondysplastic leukoplakia. Studies of larger numbers are needed to arrive at more substantial conclusions.

Carcinoma, Squamous Cell↗
PubMed1994

Joubert syndrome.

Explore the source record for details and available documents.

Cerebellar Ataxia↗
PubMed1994

Change in membrane organization induced by heat shock.

In vivo change in membrane organization in adult rat liver cells induced by heat shock was studied by incorporating the fluorescent probes 1,6-diphenyl-1,3,5-hexatriene (DPH) and 1-[4-(trimethylammonio)phenyl]-6-phenyl-1,3,5-hexatriene (TMA-DPH) in these cells. DPH was essentially localized in the plasma membrane, as indicated by quenching of its fluorescence (over 90%) by 2,4,6-trinitrobenzenesulfonate (TNBS). Measurements of both fluorescence polarization and intensity indicate that there is an immediate change in membrane organization (order) following heat shock. The polarization changes of DPH and TMA-DPH incorporated into liver cell plasma membranes upon heat shock are in opposite directions. This result is attributed to the different locations of these probes in the membrane. This change in membrane organization could be a part of a general stress response which is then transmitted to other cellular organelles.

Animals↗
PubMed1993

Restricted mobility of the sole tryptophan in membrane-bound melittin.

In spite of numerous studies, there appears to be no consensus regarding the orientation and aggregation state of membrane-bound melittin. We report here the restricted environment of the sole tryptophan residue in membrane-bound melittin using environment-induced effects on the rates of solvent relaxation. When incorporated into unilamellar vesicles of dioleoyl-sn-glycero-3-phosphocholine (DOPC), melittin exhibits a red edge excitation shift (REES) of 5 nm. In addition, fluorescence polarization of melittin in the membrane shows both excitation and emission wavelength dependence. Taken together, these observations indicate that the tryptophan residue of melittin is located in a motionally restricted region in the membrane.

Animals↗
PubMed1993

Characteristics of the eukaryotic initiation factor 2 associated 67-kDa polypeptide.

A eukaryotic initiation factor 2 (eIF-2) associated 67-kDa polypeptide (p67) protects the eIF-2 alpha-subunit from eIF-2 kinase(s) catalyzed phosphorylation, and this promotes protein synthesis in the presence of active eIF-2 kinase(s), [Datta, B., et al. (1988) Proc. Natl. Acad. Sci. U.S.A. 85, 3324-3328]. This report presents the results of studies related to characteristics of p67 action and the mechanism of p67:eIF-2 interaction: (1) p67 antibodies inhibited protein synthesis in hemin-supplemented rabbit reticulocyte lysates, and such inhibition was reversed by preincubation of the antibodies, specifically with p67. (2) p67 inhibited HRI- and dsI-catalyzed phosphorylations of the eIF-2 alpha-subunit and histones, but it did not inhibit casein kinase catalyzed phosphorylation of the eIF-2 beta-subunit. (3) p67 bound specifically to the eIF-2 gamma-subunit. p67 co-immunoprecipitated with the eIF-2 subunits when a p67/eIF-2 mixture was treated with p67 or eIF-2 subunit antibodies and protein A agarose. However, when eIF-2 was preincubated specifically with the eIF-2 gamma-subunit antibodies, subsequent co-immunoprecipitation of p67 with the eIF-2 subunits was completely inhibited. Similarly, preincubation of p67 and p67 antibodies prevented subsequent p67 binding to eIF-2. Preincubation of eIF-2, with either eIF-2 alpha- or beta-subunit antibodies, had no effect on p67 co-immunoprecipitation with the eIF-2 subunits. (4) p67:eIF-2 interaction is necessary for p67 activity to protect the eIF-2 alpha-subunit from eIF-2 kinase(s) catalyzed phosphorylation.(ABSTRACT TRUNCATED AT 250 WORDS)

Casein Kinases↗
PubMed1992

Effect of Cu(2+)-ascorbic acid on lipid peroxidation, Mg(2+)-ATPase activity and spectrin of RBC membrane and reversal by erythropoietin.

The effect of erythropoietin (Ep), a glycoprotein hormone, has been studied on lipid peroxidation induced by Cu2+ and ascorbate in vitro, Mg2+ ATPase activity and spectrin of RBC membrane. Our present investigation reveals that Cu2+ and ascorbic acid increases lipid peroxidation of RBC membrane significantly. It has further been observed that under the same experimental condition spectrin, a major cytoskeleton membrane protein, and Mg(2+)-ATPase activity of RBC membrane decrease significantly. However, exogenous administration of Ep completely restores lipid peroxidation and Mg(2+)-ATPase activity and partially recovers spectrin of RBC membrane.

Animals↗
PubMed1992

Determination of the location of fluorescent probes attached to fatty acids using parallax analysis of fluorescence quenching: effect of carboxyl ionization state and environment on depth.

In this report, parallax analysis of fluorescence quenching (see the preceding paper in this issue) was used to determine the location (depth) of anthroyloxy and carbazole probes attached to model membrane inserted fatty acids. A monotonic increase in depth was found as the number of carbon atoms between the attachment site of the probe and the fatty acyl carboxyl group is increased. It was also found that depth is sensitive to pH, with an increase in probe depth upon protonation of the fatty acid carboxyl group of around 0.5-2.5 A, depending on probe location and identity. This result shows that carboxyl protonation causes an increase in depth all along a fatty acid chain. In addition, it indicates that parallax analysis is very sensitive to small changes in depth. At a given pH, no significant change in probe depth was observed in vesicles containing anionic phospholipid or at various ionic strengths, suggesting these parameters do not strongly regulate fatty acyl chain location. It was also found that there is a decrease of the apparent depth of each of the fatty acyl attached probes both at longer excitation wavelengths and at longer emission wavelengths. This is consistent with there being a distribution of depth for each fluorophore, with shallower fluorophore dominating the fluorescence at red-shifted wavelengths. Solvent relaxation effects also appear to contribute to this wavelength dependence.

Electrochemistry↗
PubMed1992

Molecular recognition sites on factor Xa which participate in the prothrombinase complex.

Coagulation factor X, when activated to factor Xa by proteolytic cleavage, itself becomes an active serine protease which participates as a component of the macromolecular prothrombinase complex along with factor Va, phospholipid, and calcium ions. To identify specific structural regions on factor Xa responsible for mediating its function in activating prothrombin, we used 21 synthetic peptides corresponding to 65% of the primary structure of factor X as potential inhibitors of prothrombin activation. Using purified components, thrombin formation was inhibited by seven peptides in a dose-dependent noncompetitive manner. Antibodies to selected inhibitory peptides affinity purified on a factor Xa-agarose column inhibited thrombin formation in a dose-dependent manner, indicating that the corresponding regions on factor Xa are surface-exposed. Kinetic analyses varying the order of reagent addition suggested that peptides 211-222, 254-269, and 263-274 were highly effective in preventing the factor Xa-factor Va interaction. Peptides 275-287 and 415-425 were considered to derive from a distal region involved in substrate binding, based upon mixed inhibition kinetic analyses and assuming that inhibitory peptides not inhibitory in factor Va binding are related to a specific region of substrate interaction. Cross-linking studies confirmed that peptides 263-274 and 263-276 could bind specifically to the light chain of factor V/Va. These findings provide the basis for further pursuing the precise definition of interactive sites on factor Xa using site-directed mutagenesis and molecular modeling.

Amino Acid Sequence↗
PubMed1992

Aggregation of lasalocid A in membranes: a fluorescence study.

The aggregation behavior of the carboxylic ionophore, lasalocid A, has been studied in egg phosphatidylcholine vesicles by monitoring the intrinsic fluorescence of lasalocid A. Self quenching of lasalocid A fluorescence in vesicles of egg phosphatidylcholine suggests aggregation of lasalocid A. When aggregated lasalocid A is treated with increasing concentrations of lipid, there is an increase in fluorescence due to gradual reduction of self quenching on lateral dilution. This confirms the presence of loosely held non-covalent aggregates of lasalocid A in the membrane. This result is relevant in elucidating the molecular mechanism of cation transport by lasalocid A across membranes.

Cell Membrane↗
PubMed1992

The eukaryotic initiation factor 2-associated 67-kDa polypeptide (p67) plays a critical role in regulation of protein synthesis initiation in animal cells.

The eukaryotic initiation factor 2 (eIF-2)-associated 67-kDa polypeptide (p67) isolated from reticulocyte lysate protects the eIF-2 alpha subunit from eIF-2 kinase-catalyzed phosphorylation and promotes protein synthesis in the presence of active eIF-2 kinases. We have now studied the roles of p67 and eIF-2 kinases in regulation of protein synthesis using several animal cell lysates and an animal cell line (KRC-7) in culture under various growth conditions. The results are as follows. (i) Both p67 and eIF-2 kinase(s) are present in active forms in all animal cells under normal growth conditions and p67 protects the eIF-2 alpha subunit from eIF-2 kinase-catalyzed phosphorylation, thus promoting protein synthesis in the presence of active eIF-2 kinases. (ii) In heme-deficient reticulocyte lysates and in serum-starved KRC-7 cells in culture, p67 is deglycosylated and subsequently degraded. This leads to eIF-2 kinase-catalyzed eIF-2 alpha-subunit phosphorylation and thus to protein synthesis inhibition. (iii) Addition of a mitogen (namely, phorbol 12-myristate 13-acetate) to serum-starved KRC-7 cells in culture induces an increase of p67 and thus increases protein synthesis. These results suggest the following conclusions. (i) Protein synthesis inhibition in a heme-deficient reticulocyte lysate is not due to the activation of an eIF-2 kinase (heme-regulated inhibitor), as is generally believed, but is due to degradation of p67. The heme-regulated inhibitor is present in an active form and possibly in equal amounts in both heme-deficient and heme-supplemented reticulocyte lysates but cannot phosphorylate eIF-2 alpha subunit because of the presence of p67. (ii) p67 is essential for protein synthesis as it protects the eIF-2 alpha subunit from eIF-2 kinase-catalyzed phosphorylation and promotes protein synthesis in the presence of one or more active eIF-2 kinases present in all animal cells. (iii) p67 is both degradable and inducible. Only the p67 level correlates directly with the protein synthesis activity of the cell, indicating that p67 is a critical factor in protein synthesis regulation in animal cells.

Animals↗
PubMed1991

Average membrane penetration depth of tryptophan residues of the nicotinic acetylcholine receptor by the parallax method.

The membrane penetration depths of tryptophan residues in the nicotinic acetylcholine receptor from Torpedo californica have been analyzed in reconstituted membranes containing purified receptor and defined lipids. Dioleoylphosphatidylcholine and three spin-labeled phosphatidylcholines with the nitroxide group at three different positions on the fatty acyl chain were used for reconstitution of the receptor. The spin-labeled phospholipids serve as quenchers of tryptophan fluorescence. Differential quenching of the intrinsic fluorescence of the acetylcholine receptor by the spin-labeled phospholipids has been utilized to analyze the average membrane penetration depth of tryptophans by the parallax method [Chattopadhyay, A., & London, E. (1987) Biochemistry 26, 39-45]. Analyses of the quenching data indicate that the tryptophan residues on the average are at a shallow location (10.1 A from the center of the bilayer) in the membrane. In addition, the generally low levels of quenching imply that the majority of tryptophan residues are located in the putative extramembranous region of the receptor. These results are consistent with several proposed models for the tertiary structure of the acetylcholine receptor and are relevant to ongoing analyses of the overall conformation and orientation of the acetylcholine receptor in the membrane.

Acetylcholine↗
PubMed1990

Chemistry and biology of N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-labeled lipids: fluorescent probes of biological and model membranes.

Lipids that are covalently labeled with the 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD) group are widely used as fluorescent analogues of native lipids in model and biological membranes to study a variety of processes. The fluorescent NBD group may be attached either to the polar or the apolar regions of a wide variety of lipid molecules. Synthetic routes for preparing the lipids, and spectroscopic and ionization properties of these probes are reviewed in this report. The orientation of various NBD-labeled lipids in membranes, as indicated by the location of the NBD group, is also discussed. The NBD group is uncharged at neutral pH in membranes, but loops up to the surface if attached to acyl chains of phospholipids. These lipids find applications in a variety of membrane-related studies which include membrane fusion, lipid motion and dynamics, organization of lipids and proteins in membranes, intracellular lipid transfer, and bilayer to hexagonal phase transition in liposomes. Use of NBD-labeled lipids as analogues of natural lipids is critically evaluated.

4-Chloro-7-nitrobenzofurazan↗
PubMed1989

Molecular recognition in the activation of human blood coagulation factor X.

Factor X can be activated by the extrinsic activation complex (factor VIIa:tissue factor), the intrinsic activation complex (factor IXa:factor VIIIa) and by an enzyme from Russell's viper venom (RVV-X). To identify the regions on the surface of factor X that mediate its association with these three activators, we have prepared 21 synthetic peptides representing 65% of the primary structure of factor X. Only 3 of the 21 peptides inhibited the rate of factor X activation, indicating the regions represented by these three peptides are involved in factor X association. Using purified components, the rate of factor Xa formation was inhibited in a dose-dependent manner by these three peptides with the same relative potency of inhibition in each of the activation systems. The observed relative potencies were: peptide 267-283 greater than or equal to peptide 284-303 greater than peptide 417-431. Kinetic analyses indicated that the three peptides inhibited factor X activation in a non-competitive manner, and in mixed inhibitor assays the peptides were shown to be mutually exclusive of one another. In coagulation-based assays, the potency of inhibition by each peptide was decreased. However, in Russell's viper venom-X-initiated assays peptide 417-431 was the best inhibitor. Fab fragments of antibodies raised to these peptides and affinity purified on factor X-agarose columns inhibited both the purified and coagulation-based assays in a dose-dependent manner. Using the x-ray crystal structure of chymotrypsinogen as a model, these three peptides were found to be located spatially close to one another on the surface of factor X and opposite to the region where factor X is cleaved for activation. These data are consistent with a model in which the three activators combine with factor X through a recognition site composed of multiple loci that is distal to the potential cleavage site. This interaction aligns the active sites of these three enzymes in the correct orientation to cleave factor X at the same arginyl-isoleucyl bond.

Amino Acid Sequence↗