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Biomedical subjects

S Dhawan

Publications and source records attributed to S Dhawan.

At least 73 records · Page 4Linked to original sources
PubMed1991

Model for studying virus attachment. II. Binding of biotinylated human T cell leukemia virus type I to human blood mononuclear cells potential targets for human T cell leukemia virus type I infection.

Purified human T cell leukemia virus type I (HTLV-I) was biotinylated and used to study its attachment to human PBMC. The use of biotinylated HTLV-I (biot-HTLV-I) in conjunction with mouse mAb specific for selected cell-surface molecules and flow cytometric analysis allowed us to positively identify virus-binding cells among a heterogeneous blood mononuclear cell population. Biot-HTLV-I efficiently bound not only to T cells, but also to B cells and monocytes. Preincubation of monocytes with excess of unlabeled HTLV-I significantly reduced the attachment of biot-HTLV-I. HTLV-I not only bound to, but also infected, B cells, as suggested by: i) in situ hybridization of a 35S-labeled full length HTLV-I DNA probe with EBV-transformed B cells, previously cocultured with HTLV-I-producing (G11MJ) T cells, and ii) hybridization of the same nick-translated 32P-labeled DNA probe with blotted DNA from similar HTLV-I-infected EBV-transformed B cells. HTLV-I infection did not affect the ability of B cells to secrete IgG. These findings suggest that HTLV-I cannot only infect cells of the T lineage, but can also infect B cells.

Antibody Formation↗
PubMed1991

HIV-1 infection of human T lymphocytes results in enhanced alpha 5 beta 1 integrin expression.

Altered T cell adherence after human immunodeficiency virus 1 (HIV-1) infection may contribute to viral pathogenesis in the acquired immune deficiency syndrome. To address this hypothesis, we assessed mechanisms of T cell adherence to extracellular matrix proteins in vitro. We found that after HIV-1 infection, both chronically infected H9 CD4+ T cells and acutely infected primary peripheral blood lymphocytes acquired the ability to adhere to the extracellular matrix glycoprotein fibronectin, to a lesser extent to type IV collagen and laminin, but not to type I collagen. H9 cells chronically infected with two of the three HIV-1 strains studied showed approximately a sevenfold increase in attachment to fibronectin, while the same cells infected with the human retrovirus HIV-2 did not. Adhesion was accompanied by changes in morphology, including marked spreading and increased filopodia. These alterations were not blocked by the protein kinase C inhibitor H-7, which did inhibit TPA-induced T cell attachment to fibronectin. Monoclonal antibodies against both the alpha 5 and the beta 1 subunits of the classical fibronectin receptor as well as an Arg-Gly-Asp (RGD) peptide inhibited attachment, whereas anti-alpha 4 monoclonal antibodies and the CS1 peptide did not. Binding to collagen IV was also inhibited by the anti-beta 1 monoclonal antibody, but not the other antibodies. Cells metabolically labeled with [35S]methionine and analyzed by immunoprecipitation with polyclonal anti-beta 1 integrin antibody showed a 2.5-fold increase in integrin synthesis in infected cells compared to uninfected controls. This increase in synthesis was associated with an increase in cell surface expression of both alpha 5 and beta 1 integrins by FACS (registered trademark of Becton Dickinson for a fluorescence-activated cell sorter) analysis. Enhanced expression of integrins such as alpha 5 beta 1 may cause T cell adherence to a variety of tissues, where released viral gene products may induce some of the tissue-specific manifestations of HIV-1 infection.

Amino Acid Sequence↗
PubMed1991

[3H]cytisine binding to nicotinic cholinergic receptors in brain.

Cytisine, a ganglionic agonist, competes with high affinity for brain nicotinic cholinergic receptors labeled by any of several nicotinic 3H-agonist ligands. Here we have examined the binding of [3H]cytisine in rat brain homogenates. [3H]Cytisine binds with high affinity (Kd less than 1 nM), and specific binding represented 60-90% of total binding at all concentrations examined up to 15 nM. The nicotinic cholinergic agonists nicotine, acetylcholine, and carbachol compete with high affinity for [3H]cytisine binding sites, whereas among nicotinic receptor antagonists only dihydro-beta-erythroidine competes with high affinity (in the nanomolar range). Comparison of binding in several brain regions showed that [3H]cytisine binding is higher in the thalamus, striatum, and cortex than in the hippocampus, cerebellum, or hypothalamus. The pharmacology and brain regional distribution of [3H]cytisine binding sites are those predicted for neuronal nicotinic receptor agonist recognition sites. The high affinity and low nonspecific binding of [3H]cytisine should make it a very useful ligand for studying neuronal nicotinic receptors.

Acetylcholine↗
PubMed1990

A novel peptide from amyloid P component supports cell attachment.

Amyloid P component is a glycoprotein found in association with connective tissues throughout the body and is also a component of human serum. We have identified a dodecapeptide from amyloid P component which is capable of supporting the attachment of a wide variety of cells to the surface of polystyrene plastic dishes. 83% of the activity is confined to a hexapeptide, FTLCFR. Saturation of cell attachment occurs at a peptide concentration of 100 micrograms/ml used to coat the plastic. These results indicate that the active peptide may represent a functional property of amyloid P component which heretofore has no function.

Amino Acid Sequence↗
PubMed1989

Ocular changes in reactions in leprosy.

A study of ocular changes in reactions in leprosy was undertaken to assign these changes, their proper place in the wide spectrum of ocular morbidity in leprosy. 76.1% of eyes of Type I reaction and 89.7% of eyes with Type II reaction showed some ocular involvement. Corneal hypoaesthesia, superficial punctate keratitis, a decrease of corneal film break up time (BUT), prominent corneal nerves, pigment on the endothelium of the cornea and a pigmented trabecular meshwork were the common ocular findings. The incidence of iridocyclitis in Type II reactions was low (8.1%). The significance of the ocular involvement in reactions in leprosy and the pathogenesis of iridocyclitis in Type II reactions is discussed.

Adolescent↗
PubMed1987

Subunit exchange between membranous and soluble forms of bovine dopamine beta-hydroxylase.

Dopamine beta-hydroxylase is present in the bovine adrenal medulla in two forms: soluble and membrane-bound. In a previous study, it was shown that the tetrameric, soluble form of the enzyme undergoes dissociation into two identical dimeric subunits and that this subunit dissociation is dependent on pH and ADP binding (Dhawan, S., Hensley, P., Osborne, J. C., Jr., and Fleming, P. J. (1986) J. Biol. Chem. 261, 7680-7684). Here we report the effect of pH and ADP on the dissociation of the membranous form of dopamine beta-hydroxylase into two nonidentical subunits. Negative stain electron microscopy of purified membranous hydroxylase showed largely tetrameric species together with occasional dimeric species. The tetrameric images of membranous hydroxylase were similar to, but clearly different from, previously published negative stain images of soluble hydroxylase (Duong, L. T., Fleming, P. J., and Ornberg, R. L. (1985) J. Biol. Chem. 260, 2393-2398). Quantitative binding of ADP to the membranous hydroxylase revealed the existence of two binding sites per dimeric subunit. ADP binding and low pH both promote dissociation of a hydrophilic, catalytically active subunit from the membranous enzyme reconstituted onto phospholipid vesicles. Kinetic analyses of reconstituted membranous hydroxylase activity were consistent with the existence of tetrameric and dimeric catalytic species in equilibrium. All of the hydrophilic subunits of the purified soluble hydroxylase bind to the hydrophobic subunits of the reconstituted membranous hydroxylase. We propose that, in the chromaffin granules, the soluble hydroxylase subunits are in equilibrium association with the membrane-bound hydroxylase subunits and that the hydrophilic subunits of both soluble and membranous hydroxylase are identical.

Adenosine Diphosphate↗
PubMed1986

Adenosine 5'-diphosphate-dependent subunit dissociation of bovine dopamine beta-hydroxylase.

In a previous study, it was shown that purified soluble bovine dopamine beta-hydroxylase exhibits pH-dependent reversible tetramer-dimer dissociation (Saxena, A., Hensley, P., Osborne, J. C., Jr., and Fleming, P. J. (1985) J. Biol. Chem. 260, 3386-3392). Here we report evidence for the dissociation of this enzyme by magnesium-adenosine diphosphate independent of pH in the pH range 5-7. Quantitative binding of ADP to dopamine beta-hydroxylase revealed that there are two binding sites/dimeric species of hydroxylase and that ADP is tightly bound with a KD less than 10(-8) M. Kinetic data obtained at pH 5.5, the pH inside the chromaffin granule, shows that the apparent Km values for both the substrates tyramine and ascorbate are lowered by the presence of ADP without affecting the Vmax of the enzyme. The ADP-dependent lowering of apparent Km values results from a dissociation of the enzyme to the dimeric species which has inherently lower apparent Km values for substrates.

Adenosine Diphosphate↗
PubMed1983

Interaction of apolipoprotein B from human serum low-density lipoprotein with egg yolk phosphatidylcholine and cholesterol.

Binary and ternary complexes of apolipoprotein B (apo B) with egg yolk lecithin and with lecithin plus cholesterol have been formed from detergent-lipid-protein mixed micelles. These particles appear to be spherical by negative-stain electron microscopy and contain 510 000 g of protein (2 mol of apo B) complexed with apparent maximum molar ratios of 780:2 (egg yolk lecithin:apo B) and 1300:280:2 (egg yolk lecithin:cholesterol:apo B). The secondary structure as reflected in the circular dichroic spectra is similar to that of holo-LDL2 when only lecithin is bound, but is significantly altered when cholesterol is also present in the complex, suggesting that the molecular organization of the ternary complex formed in the absence of neutral lipids is significantly different from that of the native lipoprotein. A part of the protein (presumably uncharged) has to be incorporated with the lipid acyl chains in a hydrophobic "core" of the spherical particle. However, the relative amounts of apo B exposed to the aqueous solvent and to the hydrophobic interior of the recombined particles depend on the lipid content and also appear to differ from those in LDL2. The results suggest that the manner in which apo B folds is continuously variable, a result consistent with its ability to bind varying amounts of lipid in vivo.

Animals↗
PubMed1982

Conformational transitions in serum high density apoproteins of hypercholesterolemic monkeys.

Conformational transitions in serum high density apolipoproteins of normal and hypercholesterolemic monkeys have been studied by circular dichroism. This study has revealed that under hypercholesterolemic conditions the secondary structure of apolipoproteins suffers permanent changes which could be observed even after a lengthy procedure of isolation, purification and delipidation of high density lipoprotein.

Amino Acid Sequence↗
PubMed1981

Modification of phospholipid structure results in greater stability if liposomes in serum.

Previous studies have revealed that the replacement of the C-2 ester group in phosphatidylcholine by the carbamyloxy function renders the resulting lipids, without affecting the properties of the liposomes, resistant to hydrolysis by phospholipase A2 (Gupta, C.M. Bali, A. (1981) Biochim. Biophys, Acta 663, 506-515). As an extension of this work, the effect of serum on the stability of liposomes, prepared from 1-palmitoyl-2-heptadec-10-cis-enylcarbamyloxyphosphatidylcholine (carbamylphosphatidylcholine), has been examined. The stability has been measured in terms of (a) bilayer permeability to solutes, and (b) the lipid transfer to serum proteins. Replacement of egg phosphatidylcholine in liposomes by the carbamyl analog prevented serum-induced leakage of the entrapped solutes and also inhibited the lipid (phospholipid and cholesterol) transfer. Manipulation of the cholesterol content of the liposomes had no effect on the stability. These observations indicate that the interaction of serum proteins with liposomes probably involves a highly specific binding of the proteins to the liposome surface.

Animals↗
PubMed1981

Frequency and significance of fungal isolations from conjunctival sac and their role in ocular infections.

Five hundred conjunctival swabs, from 150 males and 100 females with no history of ocular infections, were collected and cultured for the isolations of fungi. Eighty (16%) of the total specimens yielded positive fungal isolations. The isolation rate was more from the males than the females subjects. Mycelial fungi were predominant than the yeast organisms. Aspergillus species were the commonest isolates with A. flavus taking the lead in the isolations being positive 16 of the total 24 Aspergillus species isolated. A variable rate of fungal isolations was observed in different months of the year. The percentage of the isolations increases after the local use of Efcorlin-N. Nineteen of the 20 eyes studied did not yield the same fungal species in the repeated samples.

Adolescent↗
PubMed1981

Isolation and mutation of cellulolytic fungi.

Nineteen fungi were isolated from different soil samples on the basis of clear zones formed on Rose Bengal Cellulose agar medium. In shake flasks th isolate K1 gave 12.1 units/ml of CMCase activity. A mutant of the isolate K1, KM7, was selected after N-methyl-N'-nitro-N-nitrosoguanidine treatment of the wild-type. This mutant differed morphologically from the parent strain on RBCA medium and gave 36.2 units/ml of CMCase activity which represented about 50% of the enzyme yield from the standard organism, Trichoderma viride QM 9414 (80 units/ml of CMCase activity). The isolate K1, which was identified as a Phoma species, produced 48 units of beta-glucosidase. The yield of beta-glucosidase was increased about 8-fold in the mutant KM7 and was about 68% higher than the level found in T. viride QM 9414.

Carboxymethylcellulose Sodium↗