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Biomedical subjects

S P Singh

Publications and source records attributed to S P Singh.

At least 19 recordsLinked to original sources
PubMed1992

Respiratory burst in peritoneal exudate cells in response to a modified tuftsin.

Intraperitoneal administration of tuftsin-M [Thr-Lys-Pro-Arg-NH-(CH2)2-NH-CO-C15H31] to Balb/C mice has been shown to induce a respiratory burst in the peritoneal exudate cells. The macrophages exhibited enhanced levels of O2-, H2O2, NADPH oxidase and myeloperoxidase, but the activities of superoxide dismutase, catalase and glutathione peroxidase remained virtually unchanged. The magnitude of the oxidative burst depended directly on the dose of tuftsin-M; higher activity was observed at higher doses of the peptide. Tuftsin-M enhanced the generation of both O2- and H2O2 under in vitro conditions, as did phorbol myristate acetate. These results suggest that tuftsin-M could enhance non-specific defence against infections by activating the macrophages.

Analysis of Variance↗
PubMed1992

Spin-labeling studies of rat liver NADPH-cytochrome p450 reductase: conformation and function relationship.

ESR spin-labeling studies designed to yield information regarding the relationship between function and conformation of rat liver NADPH-cytochrome P450 reductase (EC 1.6.4.2) were carried out. The purified enzyme was spin labeled by a nitroxide derivative of p-chloromercuribenzoate. Two conditions for spin labeling were employed: (i) the presence of NADP+, yielding an active site-protected spin-labeled reductase, and (ii) the absence of NADP+, yielding completely spin-labeled reductase. Reductase in which the active site was protected by binding NADP+ and then spin-labeled retains most of its enzymatic activity; on the other hand, completely spin-labeled reductase is devoid of any enzymatic activity. Completely spin-labeled reductase yields a two-component resolved ESR spectrum that reflects two classes of spin-labeled binding sites, a strongly immobilized (S) and a weakly immobilized (W) site. The ratio of W/S provides a valuable parameter for studying the relationship between function and conformation. Structural perturbants, such as urea, KCl, and pH, were employed to determine their effects on the activity of the enzyme and their relationship to changes in the conformational state of the reductase. It was further observed that the enzymatically active spin-labeled derivative generated superoxide radical in the presence of NADPH and cytochrome c, which in turn reduced completely the attached spin-label.

Acetylation↗
PubMed1992

Inhibition of oxytocin-stimulated phosphoinositide turnover in rat myometrium by pertussis and cholera toxins may involve protein kinase A activation.

Both pertussis and cholera toxins inhibit oxytocin-stimulated phosphoinositide turnover in rat myometrium. The actions of pertussis and cholera toxins as well as those of CPTcAMP are reversed by H-8, an inhibitor of protein kinase A. H-8 does not have a major effect on cAMP elevation by the toxins in the presence of oxytocin. The results suggest that the stimulation by oxytocin of phosphoinositide turnover does not involve direct obligatory coupling to a pertussis toxin-sensitive GTP-binding protein. Rather, indirect effects on protein kinase A activation may contribute to the inhibitory effects of both cholera and pertussis toxins. This study suggests that caution must be exercised in interpreting inhibition of phosphoinositide turnover by pertussis toxin in whole cell experiments as indicative of direct involvement of a toxin-sensitive GTP-binding protein.

Animals↗
PubMed1992

Structural relatedness of enteric bacterial porins assessed with monoclonal antibodies to Salmonella typhimurium OmpD and OmpC.

The immunochemistry and structure of enteric bacterial porins are critical to the understanding of the immune response to bacterial infection. We raised 41 monoclonal antibodies (MAbs) to Salmonella typhimurium OmpD and OmpC porin trimers and monomers. Enzyme-linked immunosorbent assays, immunoprecipitations, and/or Western immunoblot techniques indicated that 39 MAbs (11 anti-trimer and 28 anti-monomer) in the panel are porin specific and one binds to the lipopolysaccharide; the specificity of the remaining MAb probably lies in the porin-lipopolysaccharide complex. Among the porin-specific MAbs, 10 bound cell-surface-exposed epitopes, one reacted with a periplasmic epitope, and the remaining 28 recognized determinants that are buried within the outer membrane bilayer. Many of the MAbs reacting with surface-exposed epitopes were highly specific, recognizing only the homologous porin trimers; this suggests that the cell-surface-exposed regions of porins tends to be quite different among S. typhimurium OmpF, OmpC, and OmpD porins. Immunological cross-reaction showed that S. typhimurium OmpD was very closely related to Escherichia coli NmpC and to the Lc porin of bacteriophage PA-2. Immunologically, E. coli OmpG and protein K also appear to belong to the family of closely related porins including E. coli OmpF, OmpC, PhoE, and NmpC and S. typhimurium OmpF, OmpC, and OmpD. It appears, however, that S. typhimurium "PhoE" is not closely related to this group. Finally, about one-third of the MAbs that presumably recognize buried epitopes reacted with porin domains that are widely conserved in 13 species of the family Enterobacteriaceae, but apparently not in the seven nonenterobacterial species tested. These data are evaluated in relation to host immune response to infection by gram-negative bacteria.

Antibodies, Monoclonal↗
PubMed1992

Characterization of monoclonal antibodies to the outer membrane protein (OmpD) of Salmonella typhimurium.

A panel of monoclonal antibodies, seven against the trimeric and seven against the monomeric forms to outer membrane protein D (OmpD) of Salmonella typhimurium were produced. The specificities of these monoclonal antibodies for the porin proteins of S. typhimurium and their cross-reactions with Salmonella porins OmpC and OmpF were determined by Western immunoblotting and enzyme-linked immunosorbent assay. We observed that OmpD shared more epitopes and had greater structural similarity with OmpC than with OmpF.

Animals↗
PubMed1992

Protein kinase-A inhibits phospholipase-C activity and alters protein phosphorylation in rat myometrial plasma membranes.

Our previous studies implicated the involvement of protein kinase-A in the inhibitory effects of isoproterenol and relaxin on oxytocin-stimulated phosphoinositide turnover in rat myometrium. To understand the possible mechanisms involved, the properties and regulation of phospholipase-C (PLC) in purified myometrial plasma membranes from estrogen-primed rats were studied. The PLC activity measured with exogenous [3H]phosphatidylinositol 4,5-bisphosphate as substrate was Ca2+ dependent. The nonhydrolyzable GTP analog guanosine 5'-(3-O-thio)triphosphate stimulated PLC activity with a ED50 of 1.6 microM and shifted the calcium dependence curve to the left. Guanosine 5'-(3-O-thio)triphosphate-stimulated phosphatidylinositol 4,5-bisphosphate hydrolysis was inhibited by activation of endogenous and exogenous cAMP-dependent protein kinase (PKA). The effects of endogenous and exogenous PKA were significantly reversed by IP20, a potent synthetic peptide inhibitor of PKA. In the presence of [gamma-32Pi]ATP and exogenous PKA, 32Pi was incorporated in an IP20-sensitive manner into major bands at approximately 17,000, 20,000-24,000, 33,000, 38,000, 40,000-44,000, and other higher mol wt. These data indicate that one or more GTP-binding proteins mediate activation of membrane-bound PLC in rat myometrium. Phosphorylation of one or more membrane-associated proteins by PKA may regulate myometrial PLC activity and play a role in the inhibitory effects of isoproterenol and relaxin.

Adenosine Triphosphate↗
PubMed1992

Childhood diarrhoea due to rotavirus in a community.

The etiologic role of rotavirus in acute diarrhoeal illness in children under five years of age was studied over a period of one year in an urban slum community. Rotavirus was detected in 17.7 per cent of 376 children with diarrhoea and 4 per cent of 299 healthy children with maximum prevalence at 19-24 months of age with statistically comparable detection in 0-6 months of age. The overall prevalence was significantly higher in children below 2 yr as compared to those between 2-5 yr of age. Girls (24.1%) were more susceptible amongst the diarrhoeal group in comparison to boys (13.8%). Diarrhoea due to rotavirus was more prevalent during the cooler months (November-February) of the year and no correlation was observed with rainfall and relative humidity. Rotavirus as the sole pathogen was observed in 9 per cent children with diarrhoea and in the rest, association of Cryptosporidium (3%) was observed for the first time with this virus along with other known enteropathogenic bacteria and parasites, enterotoxigenic Escherichia coli being the commonest organism.

Age Factors↗
PubMed1979

13C-NMR spectra of strychnos alkaloids: brucine and strychnine.

The natural abundance 13C-NMR spectra of brucine and strychnine were obtained using the pulse Fourier transform technique. The chemical shifts of various carbon resonances were assigned on the basis of substituent effects on benzene shifts, intesities of signals, multiplicites generated in single-frequency off-resonance-decoupled spectra, and comparisons with the chemical shifts of structurally related compounds.

Chemical Phenomena↗
PubMed1979

Fourier transform carbon-13 NMR spectra of ampyrone and aminopyrine.

The natural abundance 13C-NMR spectra of ampyrone and aminopyrine were obtained using the pulse Fourier transform technique. The chemical shifts were assigned with the help of the chemical shift theory, multiplicity generated in single-frequency off-resonance decoupled spectra, relaxation time, and comparison with structurally related compounds.

Aminopyrine↗
PubMed1979

13C-NMR spectra of alpha-adrenergic blocking agents.

The natural abundance 13C-NMR spectra of five alpha-adrenergic blocking agents, tolazoline, dibenamine, azapetine, phenoxybenzamine, and phentolamine, are reported. The chemical shifts of various carbon resonances were assigned on the basis of chemical shift theory, multiplicities observed in single-frequency off-resonance-decoupled spectra, relaxation times, and comparisons with the chemical shifts of model compounds.

Adrenergic alpha-Antagonists↗
PubMed1979

Effect of ethanol and its metabolites on glucose mediated insulin release from isolated islets of rats.

Effects of ethanol and its metabolites, acetaldehyde and acetate, on insulin secretion were studied in isolated islets from normal rats. Addition of ethanol to the incubation media inhibited glucose mediated insulin release in a dose related manner. Prior exposure of islets to ethanol during the preincubation period had no influence on subsequent insulin response to either glucose or glucose plus ethanol. Acetaldehyde inhibited while sodium acetate potentiated insulin response to glucose. It is concluded that ethanol has a direct inhibitory effect on glucose mediated insulin release from rat islets.

Acetaldehyde↗