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D Pal

Publications and source records attributed to D Pal.

At least 55 records · Page 3Linked to original sources
PubMed1998

Main-chain conformational features at different conformations of the side-chains in proteins.

An analysis of the known protein structures has shown that the main-chain torsion angles, phi and psi of a residue can be affected by the side-chain torsion angle, chi1. The (chi1, psi) plot of all residues (except Gly, Ala and Pro) show six distinct regions where points are concentrated-although some of these regions are nearly absent in specific cases. The mean of these clusters can show a shift along the psi axis by as much as 30 degrees as chi1 is changed from around 180 to -60 to 60 degrees. Because of the lesser steric constraint points are more diffused along the psi axis when chi1 is approximately -60 degrees. Although points are more spread out along the phi axis in the (chi1, phi) plot, the dependence of phi on chi1 shows up in a shortened phi range (by about 30 degrees) when chi1 is around -60 degrees, and a distinct tendency of clustering of points into two regions when chi1 is approximately equal to 60 degrees, especially for the aromatic residues. Based on the dependence of the backbone conformation on its side-chain the 17 amino acids can be grouped into five classes: (i) aliphatic residues branched at the Cbeta position (although Thr is atypical), (ii) Leu (branched at the Cgamma position), (iii) aromatic residues (Trp can show some deviations), (iv) short polar residues (Asp and Asn), and (v) the remaining linear-chain residues, mainly polar. Ser and Thr have the highest inclination to occur with two different orientations of the side-chain that can be located through crystallography. Such residues exhibiting two chi1 angles have their phi and psi angles in a region that is common to the Ramachandran plots at the two different chi1 angles. The dependence of phi and psi angles on chi1 can be used to understand the helical propensities of some residues. Moreover, the average phi, psi values in the alpha-helices vary with the side-chain conformation.

Crystallography, X-Ray↗
PubMed1998

Retinoids modulate P2U purinergic receptor-mediated changes in transcervical paracellular permeability.

In human cervical cells, extracellular ATP induces an acute decrease in the resistance of the lateral intercellular space, the phase I response, followed by a delayed increase in tight junctional resistance, the phase II response. These responses depend on vitamin A because incubation of cells in retinoid-free medium (RFM) abolished both responses. Treatment with retinoic acid restored the phase I response in full, but the amplitude of the phase II response was restored only partly. Shorter incubations and lower concentrations of retinoic acid [half-maximal effective concentrations (K 1/2) = 0.1 microM] were required for restoring the phase I response than were required for reversing the phase II response (K 1/2 = 1 microM). The phase I response could be restored by ligands that bind to either retinoic acid receptors (RARs) or retinoid X receptors, but only RAR agonists had an effect on phase II response. RFM had no effect on decreases in resistance induced by ionomycin, but it attenuated phase II-like increases in resistance induced by KCl or by 1,2-dioctanoyl-sn-diglycerol (diC8). Actinomycin D blocked phase II response but not phase I response or the responses to ionomycin, KCl, or diC8. These results suggest that retinoids act on cervical cells via distinct retinoid receptor mechanisms and modulate phase I and phase II changes in resistance by regulating distinct signal mechanisms.

Adenosine Triphosphate↗
PubMed1998

Regulation by retinoids of P2Y2 nucleotide receptor mRNA in human uterine cervical cells.

Extracellular ATP stimulates acute changes in paracellular permeability across cultures of human uterine cervical epithelial cells [G. I. Gorodeski, D. E. Peterson, B. J. De Santis, and U. Hopfer. Am. J. Physiol. 270 (Cell Physiol. 39): C1715-C1725, 1996]. In this paper, we characterize mRNA for a P2Y2 nucleotide receptor in human cervical cells. Using oligonucleotide primers based on the sequence of human airway epithelium P2Y2 receptor, a single 632-bp cDNA band was identified in RT-PCR experiments in extracts of human endocervical and ectocervical tissues and in lysates of human cervical CaSki cells, but not in 3T3 fibroblasts. The nucleotide sequence was homologous to the corresponding human airway epithelium P2Y2 receptor. Northern blot analyses revealed hybridization of the P2Y2 receptor probe to a 2.0-kb mRNA fragment, as well as to 2.2-, 3. 0-, and 4.6-kb species, indicating that human cervical cells express P2Y2 receptor mRNA. Incubation of CaSki cells in retinoid-free medium abolished the ATP-induced changes in permeability and decreased the expression of the P2Y2 receptor mRNA; treatment with retinoids restored the responses to ATP and upregulated the P2Y2 receptor mRNA, suggesting that the receptor mediates ATP-related changes in permeability. Treatment with actinomycin D decreased the expression of the P2Y2 receptor RNA, but the ratio density of the receptor RNA relative to glyceraldehyde-3-phosphate dehydrogenase RNA remained unchanged, suggesting that retinoids upregulate transcription of the receptor mRNA. We conclude that retinoid-dependent modulation of the P2Y2 receptor expression, and hence of the responses to ATP, may be an important mechanism for the regulation of secretion of cervical mucus in vivo.

3T3 Cells↗
PubMed1997

Reactivation of denatured proteins by domain V of bacterial 23S rRNA.

In vitro transcripts containing domain V of the 23S rRNA of Escherichia coli and Bacillus subtilis can reactivate denatured proteins almost as efficiently as the total 23S rRNA. Here we show that almost the full length of domain V is required for reactivation of denatured pig muscle lactate dehydrogenase and pig heart cytoplasmic malate dehydrogenase: the central loop of this domain alone is not enough for this purpose. The antibiotic chloramphenicol, which binds to domain V of 23S rRNA, can inhibit reactivation of these proteins completely. Activity is eliminated by EDTA at a concentration of <1 mM, even in the presence of 4 mM MgCl2, suggesting that the three-dimensional conformation of the RNA should be maintained for this activity.

Animals↗
PubMed1997

Modulation of cellular adhesion in bovine brain microvessel endothelial cells by a decapeptide.

The importance of cell adhesion molecules in maintaining the cellular integrity of the endothelial layer is well recognized, yet their exact participation in regulating the blood-brain barrier (BBB) is poorly understood. Both Ca(2+)-dependent and Ca(2+)-independent cell adhesion molecules are found in endothelial cells. In this study, we used immunofluorescence, ELISA, Western blot and cell adhesion assay to identify a Ca(2+)-dependent cell adhesion molecule, E-cadherin, in bovine brain microvessel endothelial cells (BBMECs). Monoclonal anti-E-cadherin antibody specifically interacted with cultured BBMECs and decorated the cellular junctions with a series of punctate fluorescence spots as seen by indirect immunofluorescence using a confocal microscope. The intensity of these fluorescence spots increased after brief treatment with hIFN-gamma or CPT-cAMP. In the cellular extract of BBMECs, a 120 kDa protein was immunoprecipitated with anti-E-cadherin antibody. BBMECs did not react with anti-N-cadherin antibody, but recognized the FITC-labeled LRAHAVDVNG-NH2, a decapeptide generated from the EC-1 domain of N-cadherin, which decorated the lateral margins of the cells with fluorescence spots. A concentration-dependent binding of this decapeptide was also observed in the flow cytometry assay. BBMECs dissociated with trypsin plus Ca2+ were able to reaggregate only in the presence of Ca2+. However, such cell-cell aggregations of BBMECs were prevented by the presence of either anti-E-cadherin antibody or the decapeptide in the assay medium. These results confirm that BBMECs possess a distinct Ca(2+)-dependent cell adhesion mechanism that can be modulated by the decapeptide. This modulation of cell-cell adhesion in BBMECs by the decapeptide is thought-provoking for creating channels for paracellular drug delivery across the BBB.

Animals↗
PubMed1997

An electrophile-nucleophile interaction in metalloprotein structures.

A new attractive interaction in metalloprotein structures, between the thiolate anion of a metal-bound cysteine (acting as a nucleophile) and a carbonyl carbon of a peptide group (an electrophile), has been identified. From 82 cases extracted from 23 metalloprotein structures, the interacting S and C atoms are found to be at a distance of 3.2 (+/-2) A, such that the angle S ... C-O is 109 degrees (+/-15 degrees). Usually, the interacting atoms are from the same Cys residue, and to allow the S to interact with the carbonyl group the side-chain and the main-chain torsion angles deviate from those found in cysteines not bound by metals. There is a good correlation between the S...C distance and the angular deviation of the S...C vector from the normal to the peptide plane. Various data points may be envisaged to represent "snapshots" along the reaction coordinate for the intra-residue attack of Cys S on the CO group.

Cysteine↗
PubMed1997

Inhibition of homotypic adhesion of T-cells: secondary structure of an ICAM-1-derived cyclic peptide.

The objective of this study was to elucidate the solution conformation of cyclo-(1,12) Pen1-Pro2-Ser3-Lys4-Val5-Ile6-Leu7-Pro8-Ar g9-Gly10-Gly11-Cys12 (1) derived from the intercellular adhesion molecule-1 (ICAM-1). Cyclic peptide 1 inhibits homotypic adhesion of T-cells (Molt-3) mediated by ICAM-1 and the leukocyte function-associated antigen-1 (LFA-1) on the surface of T-cells. Cyclic peptide 1 is more potent than is the linear peptide Pen1-Pro2-Ser3-Lys4-Val5-Ile6-Leu7-Pro8-Ar g9-Gly10-Gly11-Cys12 (2) in inhibiting homotypic adhesion. The difference in biological activity of peptides 1 and 2 may be due to the more stable conformation of cyclic peptide 1 compared to linear peptide 2 or because cyclization prevents the peptide from adopting non-productive conformation. Therefore, conformational studies of cyclic peptide 1 will give a better understanding of its biological active conformation. The conformational studies of cyclic peptide 1 were done by NMR, CD and molecular dynamics simulations. NMR studies indicated that the major conformation of cyclic peptide 1 contained trans-configuration at both X-Pro peptide bonds. Type I beta-turns at Lys4-Val5-Ile6-Leu7 and Leu7-Pro8-Arg9-Gly10 were found in cyclic peptide 1. The C- and N-terminal regions of this peptide were stabilized by antiparallel beta-sheet-like structure with the presence of intramolecular hydrogen bonds. The overall structure of this peptide exposed the hydrophobic side chains on one face of the molecule and the hydrophilic side chains on the other.

Amino Acid Sequence↗
PubMed1997

Retinoids regulate tight junctional resistance of cultured human cervical cells.

The objective of the study was to determine the effect of retinoids on paracellular resistance across the cervical epithelium and the mechanisms involved. The experimental model was cultures of human CaSki cells on filters, which retain phenotypic characteristics of the endocervical epithelium. End points for paracellular resistance were measurements of transepithelial electrical resistance and fluxes of pyranine (a trisulfonic acid that traverses the epithelium via the intercellular space). Paracellular resistance was significantly increased in cells grown in retinoid-free medium; the effect could be blocked and reversed with all-trans-retinoic acid (tRA) and with agonists of RAR and RXR receptors but only partially with retinol. The effect of tRA was dose dependent and saturable, with a 50% effective concentration of 0.8 nM. The increases in paracellular resistance induced by vitamin A deficiency required longer incubation in retinoid-free medium than decreases in resistance induced by retinoic acid. tRA had only a minimal effect on paracellular resistance in cells maintained in regular medium. Retinoid-free medium increased and tRA decreased the relative cation mobility across CaSki cultures. Also the effects of tRA were nonadditive to those of cytochalasin D (which decreases tight junctional resistance) and additive to those of ionomycin (which decreases the resistance of the lateral intercellular space), suggesting that tRA modulates tight junctional resistance. It is concluded that vitamin A determines the degree of paracellular resistance across cervical cells by a mechanism that involves modulation of tight junctional resistance.

Cell Line↗
PubMed1997

Derivatives of melphalan designed to enhance drug accumulation in cancer cells.

The objective of this study was to develop chemical strategies to improve the uptake and accumulation of melphalan (L-Mel and D-Mel), a cytotoxic agent, into cancer cells. Dipeptides synthesized from L- (or D-) Mel and L-glutamic acid (L-Glu) or L-valine (L-Val) and their methyl or ethyl esters (all compounds were trifluoroacetic acid salts) were evaluated for cytotoxicity and cellular uptake using Caco-2 cells, a human colon carcinoma cell line, and RT-2 cells, a rat brain glioma cell line. Treatment of Caco-2 cells with L-Mel or D-Mel (0.5 mg/ml equivalent of melphalan) for 48 h resulted in approximately 50% cell survival. Treatment of the Caco-2 cells with dipeptide derivatives of L-Mel (or D-Mel) (11c-d, 12c-d and 13) caused similar cytotoxicity effects (approximately 50-70% of cell survival). When the cytotoxicities of the esters of L-Mel, D-Mel and their dipeptide derivatives (11a-b, 12a-b and 14) in Caco-2 cells were determined, less than 10% cell survival was observed. Similar results were observed in RT-2 cells. When the cellular uptake properties of these compounds were determined in Caco-2 cell monolayers, L-Glu-L-Mel (12c), L-Glu-D-Mel (12d), and L-Mel-L-Glu (11c) generated slightly lower intracellular levels of L-Mel or D-Mel than when the cell monolayer was treated with the amino acids (L-Mel or D-Mel). In Caco-2 cells treated with 11c, 12c or 12d, low levels of the dipeptides were also detected. Caco-2 cell monolayers treated with D-Mel-L-Glu (11d) or D-Mel-L-Val (13) showed very low levels of the amino acids (L-Mel or D-Mel), but generally higher levels of the dipeptides. In contrast to the amino acids (L-Mel, D-Mel) or the dipeptide derivatives (11c-d, 12c-d and 13), the ester derivatives of the amino acids [L-Mel(OEt), D-Mel(OEt)] or the dipeptides (11a-b, 12a-b and 14) produced 5-20 times higher intracellular concentrations of potentially cytotoxic metabolites (e.g., L-Mel, D-Mel, Mel-containing dipeptides or Mel-containing dipeptide monoesters). L-Mel(OEt), D-Mel(OEt), L-Glu(OEt)-L-Mel(OEt) (12a), L-Glu(OEt)-D-Mel(OEt) (12b), and L-Mel-L-Glu(OEt)2 (11a) accumulated mainly as either L-Mel or D-Mel, and the percentages of L-Mel or D-Mel were 99%, 99%, 90%, 75% and 98% of the total intracellular concentration of potentially cytotoxic agents, respectively. D-Mel-L-Glu(OEt)2 (11b) accumulated as its monoester (> 95%) and D-Mel-L-Val(OMe) (14) accumulated as its dipeptide metabolite (> 98%). Inclusion of Gly-Pro, carnosine, L-Phe or L-Glu did not inhibit uptake of the dipeptide derivatives of L-Mel (or D-Mel) or their esters. These results suggest that the cellular uptake of the dipeptide derivatives of melphalan and their esters is probably via passive diffusion rather than being facilitated by an amino acid transporter or a di/tripeptide transporter. The higher intracellular levels of cytotoxic agents generated from the ester derivatives of the amino acids and the dipeptides are probably due to their higher lipophilicity and the overall neutral charge of the esters and subsequent intracellular formation of the more polar amino acids (L- or D-Mel) and/or Mel-containing dipeptides. Finally, these studies suggest that dipeptides of D-Mel [11b, 11d, 13] have inherent cytotoxicity properties.

Animals↗
PubMed1996

A study of nosocomial diarrhea in Calcutta.

BACKGROUND: Nosocomial infection is a major problem in hospitalized patients, particularly those who are debilitated. These infections may manifest as diarrhea. The spectrum of infections agents causing nosocomial diarrhea in our country is not known. METHODS: Thirty-two patients, admitted to the hospital with various complaints, who developed diarrhea during their hospital stay, were studied to identify the causative agents of diarrhea. Hospital food samples were also processed for pathogens. RESULTS: The bacteria isolated from patients included established enteropathogens like Salmonella, enteropathogenic Escherichia coli, Campylobacter species and organisms with low pathogenicity like Serratia marsescens, Pseudomonas aeruginosa and Morganella morganii. The bacterial pathogens isolated were resistant to most antibiotics, suggesting their nosocomial character. Hospital food samples contained Salmonella typhimurium, Campylobacter jejuni (biotype 1) and enteropathogenic Escherichia coli, suggesting that food might have been the vehicle for these infections. CONCLUSION: Nosocomial infection was found to be an important cause of diarrhea (34%), EPEC and Salmonell being the predominant pathogens. Water, egg and milk were the source of infection in these cases. Special measures to obtain uneffected items will prevent occurrence of nosocomial diarrhea in our hospitals.

Adult↗
PubMed1995

GnRH receptor site increase on the surface of cultured gonadotropes of senescent C57BL/6NNia mice.

Anterior pituitary cells were cultured for 2 days from 6-, 14-, and 23-25-month-old C57BL/6NNia mice. The cells were then stimulated with one of three biotinylated GnRHs [biotinyl-Lys6]-[D-Lys6]GnRH, [biotinyl-Ser4]-[D-Lys6]GnRH, [biotinyl-Ser4]-[D-Trp6, des-Gly10]GnRH) at 4 degrees C for 1 h. Some of these cells were processed unfixed, attaching avidin-fluorescein and examined with fluorescent microscopy. Other cells were fixed and the biotinylated GnRH coupled to avidin-gold (20 nm particles), which was subsequently silver-enhanced (70 nm particles) and examined with light and scanning electron microscopy (SEM). To enhance the location of receptor sites for quantitation, a back-scattering electron detector was employed with the SEM. Gonadotropes from all three age groups ranged in size from 3 to 13 microns in diameter. The largest gonadotropes in each age group displayed the highest number of GnRH receptors, but the concentration/surface area (microns2) was less than for smaller cells. Smaller gonadotropes (3-6 microns diameter) from 14- and 23-25-month-old mice contained more GnRH receptor sites/microns2 (p < .001) than those from 6-month-old mice; the percentage of these gonadotropes was markedly higher for 14-(65%) and 25-(52%) versus 6-month-old (5%) mice. The number of receptor sites in larger gonadotropes (6.1-13 microns diameter) did not decline with the increasing age of the mouse. Decreased secretory activity in gonadotropes of 25-month-old mice may result from age-related changes in pituitary peptide processing or release, but it is not due to a lack of GnRH receptors or the inability of GnRH to bind to its receptor site.

Aging↗
PubMed1993

Isolation of Capnocytophaga species from non-vital anterior teeth.

Root-canal infection is very common in India. Both aerobic and anaerobic organisms have been claimed for its aetiology. However, isolation of Capnocytophaga species from non-vital anterior teeth is sparse. In this study a solitary case of Capnocytophagal root canal infection is reported.

Bacteria, Aerobic↗
PubMed1992

Topographical mapping of GnRH receptors on dispersed mouse pituitary cells by backscattered electron imaging.

Mouse anterior pituitary cells cultured for 2 days were stimulated with one of three biotinylated-GnRH probes ([biotinyl-Lys6]-[D-Lys6]GnRH, [biotinyl-Ser4]-[D-Lys6]GnRH, [biotinyl-Ser4]-[D-Trp6, des-Gly10]GnRH) in the cold (4 degrees C) for 1 hr. These cells were subsequently fixed and an avidin-gold complex was conjugated to the bound GnRH. After a second fixation, the gold label was silver-enhanced for viewing with a scanning electron microscope. Gonadotropes were identified as a result of the labeling procedure, measured for size, and the number of GnRH receptor sites counted. Gonadotropes ranged from 3 to 13 microns in diameter and contained from 23.2 +/- 3.3 to 338.4 +/- 25.2 sites per cell depending upon the size of the cell and the ligand employed. The methods described should be applicable for studying the topographical distribution of a variety of cellular receptors.

Animals↗
PubMed1992

Incidence of Campylobacter species in animal handlers.

From the stool samples collected from diarrhoeic and healthy handlers of domestic animals different Campylobacter species were isolated in 16.6 and 21.1 per cent respectively. Both biotypes 1 and 2 were identified. All the 10 strains of C. jejuni were found to be enterotoxigenic or potentially enterotoxigenic in the ligated ileal loop of albino rats.

Animal Husbandry↗
PubMed1991

Levels of alpha-inhibin in aging female mice.

alpha-inhibin was immunocytochemically localized in granulosa cells of different stages of developing follicles, freshly formed corpora lutea, and scattered interstitial cells (pigmented or ceroid cells) in ovaries of 6-, 14-, and 23-25-mo-old C57BL/6NNia mice. Developing follicles exhibited the greatest amount of staining. Quantitation of the stain using an image analysis system indicated the staining intensity within ovarian follicles of 14-mo-old mice was greater than that in 23-25-mo-old mice. The levels of plasma alpha-inhibin and estradiol (E2) decreased with age. The number of follicles present in ovaries of middle-aged mice was comparable to those of 6-mo-old mice, yet plasma levels of FSH were significantly higher than those of 6-mo-old mice. This may be due to an age-related loss in the sensitivity of the hypothalamus and/or pituitary of middle-aged mice to ovarian hormones. In contrast, ovaries of 23-25-mo-old mice contained few antral follicles and consequently produced little alpha-inhibin. There appeared to be little negative feedback regulation of FSH secretion in 23-25-mo-old mice as a result of age-related ovarian impairments. This study supports an earlier hypothesis from our laboratory [Biol Reprod 1985; 32:989-997] that the primary defect(s) limiting age-related reproductive performance in mice appears to reside within the hypothalamo-hypophyseal axis, whereas secondary defects arise from the ovary.

Aging↗
PubMed1991

Enterotoxigenicity of human and animal isolates of Campylobacter jejuni in ligated rat ileal loops.

Human and animal isolates of Campylobacter jejuni were tested for enterotoxigenicity in ligated loop of Charles-Foster rats. Of 21 isolates, 13 were proved to be toxin-positive in the initial experiments. However, the remaining 8 required one to three passages through the rat ileal loop before showing the capacity to produce enterotoxin. All isolates caused fluid accumulation comparable with the amount produced by the standard toxigenic strain of Vibrio cholerae 01 1naba 569B. The isolates of C. jejuni from human and animal sources did not show any quantitative difference in their capacity to produce enterotoxin.

Animals↗