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Biomedical subjects

D Singh

Publications and source records attributed to D Singh.

At least 163 records · Page 9Linked to original sources
PubMed1997

CD, absorption and thermodynamic analysis of repeating dinucleotide DNA, RNA and hybrid duplexes [d/r(AC)]12.[d/r(GT/U)]12 and the influence of phosphorothioate substitution.

Circular dichroism (CD) spectra and melting temperature (Tm) data for five duplexes containing phosphorothioate linkages were compared with data for four unmodified duplexes to assess the effect of phosphorothioate modification on the structure and stability of DNA. DNA and DNA.RNA duplexes. Nine duplexes were formed by mixing oligomers 24 nt long in 0.15 M K+(phosphate buffer), pH 7.0. Unmodified DNA.DNA and RNA.RNA duplexes were used as reference B-form and A-form structures. The CD spectra of the modified hybrids S-d(AC)12.r(GU)12 and r(AC)12.S-d(GT)12 differed from each other but were essentially the same as the spectra of the respective unmodified hybrids. They were more A-form than B-form in character. CD spectra of duplexes S-d(AC)12.d(GT)12 and d(AC)12.S-d(GT)12 were similar to that of d(AC)12.d(GT)12, except for a reduced long wavelength CD band. Sulfur modifications on both strands of the DNA duplex caused a pronounced effect on its CD spectrum. The order of thermal stability was: RNA.RNA > DNA.DNA > DNA.RNA > S-DNA.DNA > S-DNA. RNA > S-DNA.S-DNA. Phosphorothioation of one strand decreased the melting temperature by 7.8+/-0.6 degrees C, regardless of whether the substitution was in a hybrid or DNA duplex. Thermodynamic parameters were obtained from a multistate analysis of the thermal melting profiles. Interestingly, the destabilizing effect of the phosphorothioate substitution appears to arise from a difference in the entropy upon forming the DNA.DNA duplexes, while the destabilizing effect in the DNA.RNA hybrids appears to come from a difference in enthalpy.

Circular Dichroism↗
PubMed1997

Physiological and biochemical characterization of intergeneric hybrids of thermotolerant and non-thermotolerant yeasts.

Kluyveromyces-like intergeneric hybrids of thermotolerant Kluyveromyces marxianus and non-thermotolerant Saccharomyces cerevisiae, produced in a previous study by protoplasmic fusion, have been characterized. On molasses, these strains produced ethanol in excess of 6% (v/v) both at 30 and 45 degrees C as against 3% and 4.2% (v/v) by the former parent at 30 and 45 degrees C, respectively. In hybrids, the increase in ethanol production appeared to be a sequel to increased activities of alcohol dehydrogenase and pyruvate kinase, derived probably from S. cerevisiae parent. Hybrid ADH-isozyme pattern on polyacrylamide gel corroborated the presence of S. cerevisiae ADH in the tested hybrids. Regression analyses indicated a positive correlation between ethanol production and ADH or PK or both (r approximately 0.76-0.84).

Hybridization, Genetic↗
PubMed1997

Characterization of the Na+/H+ exchanger in human choriocarcinoma (BeWo) cells.

We examined the expression and activity of the Na+/H+ exchanger in the human choriocarcinoma BeWo cell line. When treated with methotrexate, these cells differentiated from cytotrophoblast-like cells to enlarged multinucleate syncytiotrophoblast-like cells. There was no change in the apparent Km for Na+ between undifferentiated and differentiated cells. However, differentiated cells could transport more than five times the proton flux of undifferentiated cells. There was no difference in the Hill coefficient between undifferentiated and differentiated cells. However, the maximal flux (Jmax) for undifferentiated cells was higher than that for differentiated cells. Inhibition of Na+/H+ exchange activity by an amiloride analog and Hoe694 revealed a sensitive and a resistant component in both differentiated and undifferentiated cells. Northern blot analysis and immunocytochemistry suggested that the sensitive component was due to the NHE1 isoform of the protein while the resistant component was due to the NHE3 isoform. The NHE1 isoform was localized to the brush border membrane of BeWo cells and Western blot analysis showed that the NHE1 protein was more abundant in brush border membranes from differentiated BeWo cells compared to undifferentiated cells. The results show that BeWo cells contain the NHE1 and NHE3 isoforms of the Na+/H+ exchanger and that the NHE1 isoform is primarily localized to the brush border membrane.

Blotting, Northern↗
PubMed1997

Active vision therapy for pseudophakic amblyopia.

PURPOSE: To study the benefit of active vision therapy using various pleoptic methods in pseudophakic amblyopic children and young adults. SETTING: Daljit Singh Eye Hospital, Amritsar, India. METHODS: This study comprised 160 consecutive pseudophakic amblyopic patients who had had iris-claw lens implantation for congenital or traumatic cataract. Their ages ranged from 3.5 to 25.0 years. Before active vision treatment, visual acuity was worse than 20/200 in 63 patients (39.3%), 20/200 in 77 (48.1%), 20/120 to 20/80 in 14 (8.7%), and 20/60 in 6 (3.7%). The methods included Haidinger brushes on the synoptophore, after images, CAM stimulator, drawings on the cheiroscope, Pigeon-Cantonnet stereoscope, video games with the amblyopic eye, and exercises for promoting eye-hand coordination. Mean duration of therapy was 6 months. RESULTS: After therapy, visual acuity was worse than 20/200 in 31 patients (19.4%), 20/200 in 38 (23.7%), 20/120 to 20/80 in 41 (25.6%), 20/60 to 20/40 in 36 (22.5%), and 20/20 in 14 (8.7%). In 20 patients (12.5%), all younger than 15 years, visual acuity decreased within 1 month after treatment stopped. However, vision was rapidly restored after another session of active vision therapy. CONCLUSIONS: Active vision therapy helped improve visual acuity in the majority of young pseudophakic amblyopes.

Adolescent↗
PubMed1997

Immediate breast reconstruction in patients with locally advanced disease.

Immediate breast reconstruction for patients with early-stage disease is well established. This study evaluates a consecutive series of 22 patients with locally advanced disease (stage IIB or III) who underwent mastectomy and immediate breast reconstruction. All patients received several cycles of neoadjuvant chemotherapy (average, 3.5 cycles) followed by completion of chemotherapy beginning approximately 3 weeks following surgery. The perioperative morbidity was 14% and no patient suffered a delay in the resumption of chemotherapy. Patients have been particularly grateful about being offered reconstruction in this setting. Our preliminary results with this technique have been encouraging and further study is warranted.

Adult↗
PubMed1997

Sequencing of heat shock protein 70 (DnaK) homologs from Deinococcus proteolyticus and Thermomicrobium roseum and their integration in a protein-based phylogeny of prokaryotes.

The 70-kDa heat shock protein (hsp70) sequences define one of the most conserved proteins known to date. The hsp70 genes from Deinococcus proteolyticus and Thermomicrobium roseum, which were chosen as representatives of two of the most deeply branching divisions in the 16S rRNA trees, were cloned and sequenced. hsp70 from both these species as well as Thermus aquaticus contained a large insert in the N-terminal quadrant, which has been observed before as a unique characteristic of gram-negative eubacteria and eukaryotes and is not found in any gram-positive bacteria or archaebacteria. Phylogenetic analysis of hsp70 sequences shows that all of the gram-negative eubacterial species examined to date (which includes members from the genera Deinococcus and Thermus, green nonsulfur bacteria, cyanobacteria, chlamydiae, spirochetes, and alpha-, beta-, and gamma-subdivisions of proteobacteria) form a monophyletic group (excluding eukaryotic homologs which are derived from this group via endosybitic means) strongly supported by the bootstrap scores. A closer affinity of the Deinococcus and Thermus species to the cyanobacteria than to the other available gram-negative sequences is also observed in the present work. In the hsp7O trees, D. proteolyticus and T. aquaticus were found to be the most deeply branching species within the gram-negative eubacteria. The hsp70 homologs from gram-positive bacteria branched separately from gram-negative bacteria and exhibited a closer relationship to and shared sequence signatures with the archaebacteria. A polyphyletic branching of archaebacteria within gram-positive bacteria is strongly favored by different phylogenetic methods. These observations differ from the rRNA-based phylogenies where both gram-negative and gram-positive species are indicated to be polyphyletic. While it remains unclear whether parts of the genome may have variant evolutionary histories, these results call into question the general validity of the currently favored three-domain dogma.

Amino Acid Sequence↗
PubMed1997

Fine mapping of an imprinted gene for familial nonchromaffin paragangliomas, on chromosome 11q23.

Hereditary nonchromaffin paragangliomas (PGL; glomus tumors; MIM 168000) are mostly benign, slow-growing tumors of the head and neck region, inherited from carrier fathers in an autosomal dominant fashion subject to genomic imprinting. Genetic linkage analysis in two large, unrelated Dutch families assigned PGL loci to two regions of chromosome 11, at 11q23 (PGL1) and 11q13.1 (PGL2). We ascertained a total of 11 North American PGL families and confirmed maternal imprinting (inactivation). In three of six families, linkage analysis provided evidence of linkage to the PGL1 locus at 11q23. Recombinants narrowed the critical region to an approximately 4.5-Mb interval flanked by markers D11S1647 and D11S622. Partial allelic loss of strictly maternal origin was detected in 5 of 19 tumors. The greatest degree of imbalance was detected at 11q23, distal to D11S1327 and proximal to CD3D. Age at onset of symptoms was significantly different between fathers and children (Wilcoxon rank-sum test, P < .002). Affected children had an earlier age at onset of symptoms in 39 of 57 father-child pairs (chi2 = 7.74, P < .006). However, a more conservative comparison of the number of pairs in which a child had > or = 5 years earlier age at onset (n = 33) vis-a-vis that of complementary pairs (n = 24) revealed no significant difference (chi2 = 1.42, P > .2). Whether these data represent genetic anticipation or ascertainment bias can be addressed only by analysis of a larger number of father-child pairs.

Adolescent↗
PubMed1997

Osteoclasts constitutively express regulators of bone resorption: an immunohistochemical and in situ hybridization study.

Bone resorption is controlled by the local production of soluble regulatory molecules within the marrow microenvironment that mediate osteoclast recruitment, differentiation, and activation. Under normal conditions osteoclasts are rarely seen; in many pathologic states, however, the number of osteoclasts is dramatically increased, resulting in a net-loss of bone mass. The role of the osteoclasts as autocrine regulators of bone resorption in either normal or pathologic conditions has not been extensively investigated. The expression of IL-1 beta, IL-6, and TNF-alpha was examined in osteoclasts by immunohistochemistry under conditions of normal, reactive, and pathologic bone resorption, including growth plate (3 cases), fracture callus (5 cases), osteomyelitis (3 cases), Paget's disease (6 cases), giant-cell tumor of bone (14 cases), and brown tumor of hyperparathyroidism (2 cases). In each case, osteoclasts demonstrated immunoreactivity for IL-1 beta, IL-6, and TNF-alpha. In areas of active bone resorption, the intensity and uniformity of staining among the various conditions were similar, suggesting constitutive expression of these cytokines by activated osteoclasts. Giant-cell tumors of bone showed cytokine reactivity in over half of the giant cells, whereas stromal cells showed scattered staining. In acute osteomyelitis, inflammatory cells (mainly macrophages) and osteoclasts were intensely positive for all three cytokines. The immunohistochemical findings were confirmed by in situ hybridization using probes specific for IL-6 and TNF-alpha, the pattern of mRNA expression paralleled that of immunoreactivity for these cytokines. These findings support the notion of autocrine/paracrine regulation of bone remodeling by osteoclasts. Because overproduction of these cytokines may enhance bone resorption through the stimulation of osteoclast progenitor cells as well as mature osteoclasts, pathologic bone lesions with a large increase in the number of osteoclasts may be self-perpetuating. Alteration in the synthesis, secretion, or activity of these important regulatory molecules may in turn alter bone remodeling and loss.

Bone Diseases↗
PubMed1997

Offspring sex ratio in women with android body fat distribution.

The relationship between waist-to-hip ratio (WHR), several behavioral factors, and the number of male and female offspring was examined in a sample of 69 women. Two questions were examined: (1) Are hormonal differences, as indicated by differences in the WHR, associated with offspring sex ratio? and (2) are there any behavioral factors, such as coital frequency or orgasm, that are associated with offspring sex ratio? After statistically controlling for subject's age, socioeconomic status, and total number of offspring, we found that women with a higher WHR tended to have more sons than daughters. In addition, women who reported greater ease of having multiple orgasms also tended to have more sons than daughters. The results thus support both a hormonal and a behavioral influence on offspring sex ratio.

Adult↗
PubMed1996

Structure and analysis of the mouse Na+/H+ exchanger (NHE1) gene: homology and conservation of splice sites.

The Na+/H+ exchanger is a widely distributed integral membrane protein that is responsible for pH regulation in mammalian tissues. We have cloned and analyzed the NHE1 isoform of the mouse genomic Na+/H+ exchanger. A clone from a mouse genomic library contained the NHE1 promoter region and the 5'-untranslated region. It also contained the first 121 amino acids of the coding region of the Na+/H+ exchanger. A splice site occurred after amino acid 121, at the same region as in the human NHE1 gene. The deduced amino terminal coding sequence was 76 and 88% identical to the human and rat NHE1 sequences respectively. The 5'-untranslated region was highly homologous to that of other species and two minicistrons contained in the human Na+/H+ exchanger were present in the mouse sequence. The results show that the deduced protein sequence of the mouse NHE1 gene has a high level of homology with other species and that the splice site of the first intron is conserved. These results suggest that the first large intron may play an important role in the NHE1 gene expression.

Amino Acid Sequence↗
PubMed1996

Role of N-terminal domain of streptokinase in protein transport.

Streptokinase (SK), an extracellular protein of several haemolytic strains of Streptococcus, is utilized as a potent thrombolytic agent for the treatment of various myocardial disorders. Functional properties of SK remain unchanged when the first 13 N-terminal amino acid (aa) residues are removed. At present, role of this segment in protein structure function is unclear. skc gene encoding for the mature SK and its deletion variant, lacking its first 13 aa residues, were cloned and expressed in E. coli. Full length SK, deprived of any leader sequences, was able to translocate slowly, across the cyto-plasmic and outer membranes of E.coli. Whereas, SK derivative, devoid of its first 13 N-terminal aa residues, could not do so. Cell fractionation studies as well as genetic evidences utilizing alkaline phosphatase fusion, point towards the existence of additional information for protein transport, within the N-terminal domain of SK. To further investigate the role of this region in protein secretion, genetic fusions were created in between full length and 13 aa deleted SK with OmpA leader peptide. Studies on kinetics of SK export from E.coli, revealed that translocation of protein is 3-4 times faster when the first 13 N-terminal residues of SK are intact. On the basis of results obtained, it has been proposed that the N-terminus of mature SK maintains the export competent status of protein and, thus, confer speed and efficiency upon the translocation process of streptokinase.

Biological Transport↗
PubMed1996

The use of histone as a facilitator to improve the efficiency of retroviral gene transfer.

Vectors based on murine C-type retroviruses are commonly used in biology. The efficiency of viral infection is normally increased by a facilitator, for example polybrene, DEAE-dextran or a liposome. The receptor for ecotropic viruses is a transporter for basic amino acids; we therefore explored the use of a highly basic protein, histone type IIA, as a facilitator. We show in several cell types that histone is as efficient as the other agents tested, and in some cases more so. This readily available reagent is thus likely to be useful in the wide range of studies that employ retroviral vectors.

Amino Acids, Diamino↗
PubMed1996

Callosities, corns, and calluses.

Inappropriate shoes, abnormal foot mechanics, and high levels of activity produce pressure and friction that lead to corns and calluses. Most lesions can be managed conservatively by proper footwear, orthoses, and, if necessary, regular paring. The lesions usually disappear when the causative mechanical forces are removed. Surgery is rarely indicated and should be specifically aimed at correcting the abnormal mechanical stresses.

Callosities↗
PubMed1996

Atrial fibrillation in acute myocardial infarction: a prospective study based on data from a consecutive series of patients admitted to the coronary care unit.

Atrial fibrillation (AF) is a common and much-studied arrhythmia in patients with acute myocardial infarction (MI). However, documentation of its occurrence in temporal association with MI has been often neglected in the literature; also, its frequent occurrence with mere advanced age, or in the setting of various cardiac conditions or complications, has prevented the definition of an exact role for AF as a marker or determinant of outcome in patients with MI. The purpose of this study was to evaluate prospectively the frequency of AF (present or occurring subsequently) in a consecutive series of patients with MI admitted to the Coronary Care Unit, and to explore for variables associated with this arrhythmia; the role of AF in determining major clinical outcomes of the patients was also examined. A large data base of baseline, clinical, laboratory, and patient outcome variables was generated and continuously updated to examine correlates of AF and its possible role in determining prognosis. AF was found in 72 of 517 patients, of whom 58 experienced this arrhythmia anew. Univariate analyses detected a positive association of AF with age, pulmonary congestion, left ventricular hypertrophy, high admission Killip class, and a large array of complications including in-hospital mortality. Multivariate analyses showed, however, that AF correlated weakly with age and strongly with left ventricular hypertrophy and occurrence of ventricular tachycardia, but that it was not a determinant of ventricular fibrillation or in-hospital mortality.

Age Factors↗
PubMed1996

Process optimization for continuous ethanol fermentation by alginate-immobilized cells of Saccharomyces cerevisiae HAU-1.

Continuous ethanol production by immobilized cells of Saccharomyces cerevisiae HAU-1 has been studied using synthetic and molasses based medium in column reactors. Immobilization of 30% yeast cells biomass (wet) in 1.5% calcium alginate gel resulted in the production of 20.8 g. l-1.h-1 alcohol at a dilution rate of 0.36 h-1 with approximately 1/3rd volume of the column reactor packed with gel beads. Optimum diameter of the beads was found to be 3.5 mm for efficient fermentation. The size of the column reactor (length to diameter ratio) also affected the productivity and fermentation efficiency due to gas hold-up and mass transfer effects. Molasses could also be fermented by this system but at a lower fermentation efficiency which could be improved, to some extent, by supplementation with nutrients.

Alginates↗
PubMed1996

Triorganosilicon (IV) compounds: synthesis, structural study, and biological activity.

A few coordination compounds of silicon (IV) have been synthesized by the interaction of trimethyl- and triphenyl-chlorosilane with nitrogen-sulphur donor ligands. These compounds are monomeric, as indicated by molecular weight determination, and they behave as nonelectrolytes in dry DMF. From the electronic, infrared, 1H, and 13C NMR spectral results, it has been concluded that in these compounds, silicon is penta-coordinated in a trigonal bipyramidal environment. An assessment of biological activity of these compounds has shown that some of them are very active against P. mirabilis and others against S. viridans bacteria, while all of them show good fungicidal action against F. oxysporum, A. alternata, and A. niger.

Alternaria↗
PubMed1996

Effect of cataract on corneal topography results.

This report details the case of a 65-year-old man with advanced cataract in which there was a large discrepancy between the K-readings taken with a keratometer and those taken with a TMS-1 videokeratoscope. It was suspected the discrepancy was caused by the advanced cataract in the presence of a dilated pupil. Repeat videokeratoscopic readings were close to the standard keratoscopic readings. This finding indicates that corneal topography can be affected by reflections other than those from the corneal surface.

Aged↗