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Biomedical subjects

P K Nandi

Publications and source records attributed to P K Nandi.

At least 19 recordsLinked to original sources
PubMed1992

Mechanism of entry of a xenotropic MMuLV-derived recombinant retrovirus into porcine cells using the expression of the reporter nlslacZ gene.

A xenotropic Moloney murine leukemia virus-derived recombinant retrovirus (MMuLVSVnlslacZ) has been utilized to study the mechanism of virus entry into endothelial and epithelial porcine cells. In the genome of this recombinant retrovirus, the nlslacZ reporter gene is under the transcriptional control of both LTR and SV40 early promoter. The entry of the retrovirus has been determined from the expression of this transduced reporter gene after its integration into the infected cells. This allows the detection of a very low level of viral infection and hence entry of the virus. Exposure of the virus-cell mixture to acidic pH (less than 6) during the early phase of interaction reduces the level of internalization. Cellular infection in presence of weak bases, ammonium chloride and amantadine and an ionophore monensin at concentrations sufficient to neutralize the endosomal pH does not modify the extent of viral entry into the cells. The results indicate that the entry of the recombinant retrovirus into porcine cells takes place by a pH-independent viral membrane-cell plasma membrane fusion mechanism.

Amantadine↗
PubMed1990

Physiological responses of Vicia faba plants to sulfur dioxide.

Exposure of broad bean (Victa faba L.) plants to 270 +/- 32 and 670 +/- 45 micrograms m 3SO2 for 1.5 hr daily between 40 and 85 days of their ages resulted in an increase in their transpiration rate, water saturation deficit, phenol content, and peroxidase activity and a decrease in protein content. With the increase in number of exposures of plants to SO2, chlorotic and brown, necrotic visible injury signs were also developed in leaves. It was further noted that the magnitude of undesirable biochemical changes, which possibly helped in the formation of new pigment characteristic of necrotic tissue of SO2-exposed plants, was not totally dependent on the pollutant concentration.

Aging↗
PubMed1987

Fusion of negatively charged liposomes with clathrin-uncoated vesicles.

The interaction of lipid vesicles with uncoated vesicles from bovine brain has been studied by fluorescence energy transfer between fluorescent lipid analogs (NBD-PE, Rh-DOPE), by loss of fluorescence self-quenching (NBD-PE, carboxyfluorescein) and by freeze-fracture electron microscopy. The fluorescence techniques monitor the mixing of membranous lipids and the induced release of encapsulated material. The results demonstrate a mixing of the negatively charged lipid (PA, PS) vesicles with the uncoated vesicles. In parallel with the lipid mixing a release of intravesicularly encapsulated material takes place. Lipid vesicles composed of zwitterionic lipids (PC, DOPC, PC:PE) do not specifically interact with uncoated vesicles. The electron micrographs reveal single fusion events. Studies on the kinetics are consistent with a fusional mechanism of the negatively charged lipid vesicles with uncoated vesicles.

Animals↗
PubMed1987

Interaction of negatively charged liposomes with nuclear membranes: adsorption, lipid mixing and lysis of the vesicles.

Fluorescence energy transfer studies reveal that negatively charged lipid vesicles interact with nuclei from mouse liver cells. This interaction was observed with charged lipid vesicles composed of PA or PS but not with the uncharged PC or PE:PC vesicles. The vesicles were prepared by bath sonication and contained either a fluorescent marker in the lipid bilayer or in the vesicular interior. The negatively charged vesicles showed an adsorption to the nuclear membrane visible by fluorescence microscopy. The results obtained by resonance energy transfer experiments are interpreted in terms of a mixing of the lipids from the vesicles with the nuclear membrane. Encapsulation studies documented a staining of the nuclei only if the dye molecules of high or low molecular weight were encapsulated inside negatively charged vesicles. As consequence of the vesicle-nuclei interaction morphological changes on the nuclear surface became visible.

Adsorption↗
PubMed1986

Biologically active, recombinant DNA in clathrin-coated vesicles isolated from rat livers after in vivo injection of liposome-encapsulated DNA.

DNA entrapped in liposomes containing lactosylceramide in the bilayers is found to be associated with clathrin-coated vesicles isolated from the rat livers after intravenous injection of these liposomes. The presence of the exogenous DNA in the coated vesicles was detected by Southern blotting. The amount of DNA present in the coated vesicles does not appear to vary up to 4 h after injection of the liposomes into the animals. The recognition of the lactosyl group present in the liposome by the galactose receptor present on the surface of the different liver cells may lead to their internalization in a way analogous to receptor-mediated endocytosis of various macromolecules. DNA present in the lumen of the coated vesicles is found to be biologically active as evidenced by its replication in bacterial cells and mouse fibroblasts.

Animals↗
PubMed1985

The stability and transitions of tryptic-digested clathrin.

The pH-dependence of dissociation of trypsin-digested baskets has been determined by light scattering and compared with that of undigested baskets. Essentially no difference was found between the two types of baskets. The molecular transitions of clathrin derived from digested baskets have been studied by fluorescence spectra and polarization measurements and compared with those of undigested baskets. The transitions in both forms of clathrin were very similar. It is clear, therefore, that removal of about 1/3 of the mass from the distal portions of the arms of the clathrin triskelion does not affect its structural transitions. The interactions between clathrin molecules in the basket structure and those within the molecule appear, therefore, to remain intact in the smaller clathrin chains remaining after tryptic digestion. The function of the distal portion of the clathrin chain still awaits elucidation.

Biophysical Phenomena↗
PubMed1985

Destabilization of collagen structure by amides and detergents in solution.

The effects of amides and detergents on collagen to gelatin transition have been studied at neutral pH. Simple amides denature the protein. The substitution of H-atoms by the alkyl groups at the nonpolar end of amide increases the effectiveness of the compounds in destabilizing the collagen structure whereas substitution of the H-atom at the polar amide end shows marginal effects on the collagen transition. The capabilities of these reagents to denature collagen are much less pronounced than their effects on denaturing globular proteins. Anionic detergents are found to destabilize collagen at very low concentrations (below their cmc values). In this respect, the effects of the detergents on collagen are comparable to the denaturing effects of the detergents on globular proteins. The effect of detergents increases with the increase in the length of the alkyl chain. The structure of the anion in the detergent is also important as seen from the lower potency of the sulfonate containing detergent compared to the sulfate containing detergent in denaturing collagen. Cationic and nonionic detergents do not denature collagen.

Amides↗
PubMed1978

Dissociation, aggregation of sesame alpha-globulin in nonionic detergent solution.

Nonionic detergents Triton X-100 and Brij 36T induce dissociation and aggregation of the protein sesame alpha-globulin above the critical micelle concentrations (cmc) of the detergents. Spectrophotometric titration in Triton shows no change in the pKInt value of the tyrosyl groups at 1x10-3 M detergent where both dissociation and aggregation of the protein are observed. Fluorescence measurement does not indicate any change in the environment of the tryptophan groups of the protein in Brij. Viscosity measurements show no major conformational change of the protein in the detergent solution. Binding measurements suggest that perhaps micelles of the detergent predominantly bind to the protein. The detergent micelles preferentially bind to the exposed hydrophobic surfaces of the protein subunits. The association of the protein detergent complex through electrostatic interaction is probably responsible for the formation of the aggregates.

Alpha-Globulins↗
PubMed1977

Association-dissociation behavior of sesame alpha-globulin in electrolyte solutions.

The major protein fraction, alpha-globulin, of sesame seed (Sesamum indicum L.) contains subunits which are associated predominantly by hydrophobic interactions. Effects of various salts show the following effectiveness of anions in dissociating the proteins, SO4(2-) less than Cl- less than Br- less than ClO4- less than SCN- less than or equal to I- less than CCl3COO-, the first two members being association-inducing ions. CCl3COONa is found to be the most effective among the series in causing dissociation. The cations Li+, Na+, K+, and Cs+ induce association, the order of effectiveness being Cs+ approximately K+ greater than or equal to Na+ greater than Li+. The low concentration of salts (anions) necessary to induce dissociation does not involve a detectable change in protein conformation. The discrepancy between the effectiveness of the anions in dissociating the protein and the Hofmeister pattern of these ions has been discussed.

Globulins↗
PubMed1977

Aggregation, dissociation and denaturation of sesame (Sesamum indicum L.) alpha-globulin in cetyl trimethyl ammonium bromide solution.

The behaviour of the major protein of sesame seed (Sesamum indicum L.) alpha-globulin has been studied in a cationic detergent, cetyl trimethyl ammonium bromide solution. Up to a critical detergent concentration the protein is precipitated from solution, above which redissolution of the protein is observed. Sedimentation velocity patterns indicate the presence of higher aggregates in the detergent concentration range 5 X 10(-5)--1 X 10(-3) M. These are considered to be the soluble precursors of the insoluble aggregates. Fluorescence measurements show that tryptophanyl groups of the protein which are in contact with the aqueous phase are perturbed by the detergent. The difference spectra of the protein in higher concentration of detergent indicate considerable red shift in the spectrum. Spectrophotometric titration of phenolic groups in 1 X 10(-2) M CTAB indicate that a conformational change in the protein has taken place.

Alpha-Globulins↗
PubMed1977

Dissociation, aggregation and denaturation of sesame alpha-globulin in urea and guanidine hydrochloride solutions.

The effect of urea and GuHCl on the major protein of sesame seed (Sesamum indicum L.), alpha-globulin, has been investigated by turbidity, sedimentation velocity, viscosity, difference spectra and fluorescence spectral measurements. The protein undergoes dissociation, aggregation and denaturation in the presence of the above denaturants. There is a critical concentration of the denaturant where aggregation is maximum. Both denaturation and aggregation are lower in buffers of high ionic strength. Dissociation and aggregation have been explained by considering two types of subunits present in the protein molecule, one leading to smaller sedimenting component and the other producing the aggregate. The amino acid analysis shows that the aggregated fraction is rich in aliphatic amino acid residues. The endothermic nature of the aggregation process has been considered to arise from hydrophobic interaction of aliphatic side chains of the relevant subunits. The protein exists in a more denatured state in GuHCl than in urea solution.

Amino Acids↗
PubMed1977

Association-dissociation and denaturation behaviour of an oligomeric seed protein alpha-globulin of Sesamum indicum L. in acid and alkaline solutions.

The association-dissociation and denaturation behaviour of the major protein fraction, alpha-globulin of sesame seed (Sesamum indicum L.), in acid and alkaline solutions in the ranges of pH 4.2-1.5 and pH 7-12 have been studied. The results of gel filtration, fluorescence and viscosity measurements indicate dissociation and denaturation of the protein up to pH approximately 3. The difference spectrum in this region arises from a combination of dissociation, denaturation and charge effect on the chromophore. In still stronger acid solution, reassociation of the dissociated fraction takes place by hydrophobic interaction. In alkaline solution dissociation takes place around pH 8, and above pH 10 dissociation and denaturation proceed simultaneously as has been evidenced by sedimentation, fluorescence, spectral change, optical rotation and viscosity measurements. The phenolic group (pKInt=10.6) in the protein is abnormal and denaturation in alkaline solution is irreversible. Above pH 11.5 further dissociation of the protein takes place. Characteristic pH values of transition from 10.6-10.8 indicate that the transition of the protein involves a single step in alkaline solution.

Acids↗
PubMed1976

Thermodynamic parameters of transfer of N-acetyl ethyl esters of different amino acids from organic solvents to water.

The distribution coefficients of N-acetyl ethyl esters of glycine, diglycine, beta-alanine, alanine, valine, norvaline, leucine and norleucine between water and different organic solvents have been measured at different temperatures. Similar distribution coefficients have been measured for simple amides, urea, formamide, acetamide and N-methyl acetamide. From the distribution measurements, deltaGtr, the free energy of transfer of the solutes from organic solvents to water has been calculated. The temperature dependence of the distribution coefficient values has been utilised to determine the enthalpy of transfer, deltaHtr, and entropy of transfer deltaStr for the above process. From these results similar thermodynamic parameters for the transfer of different nonpolar side chains and peptide groups have been determined and compared with the available data in the literature.

Acetamides↗
PubMed1976

Dissociation and denaturation behaviour of sesame alpha-globulin in sodium dodecyl sulphate solution.

The effect of anionic detergent, sodium dodecyl sulphate, on the major protein, alpha-globulin of sesame seed (Sesamum indicum L.) has been investigated by gel filtration, sedimentation velocity, viscosity, optical rotation, difference spectra and fluorescence measurements. The detergent causes dissociation of the protein first and then denaturation. In the detergent concentration range of .175-4.0 X 10(-"3) M four components are observed in the ultracentrifuge. The specific rotation of the protein increases with the detergent concentration above 2.5 x 10 (-3) M detergent suggesting conformational change; above 8 X 10(-"3) M detergent the value of -[alpha] does not change. The reduced viscosity etared however, increases above .25 X 10(-3) M detergent and does not attain a plateau value. The difference spectrum of the protein indicates that both tryptophan and tyrosine groups have been affected by the detergent. The fluorescence intensity decreases and the maxima shifts towards red in the detergent solution resulting in an "isoemissive point" at 355 nm. The double difference spectra in sucrose-detergent protein system show that below 5-0 X 10(-3) M detergent, the difference absorption and fluorescence spectrum result from the binding of the detergent near the chromophoric groups and are not due to conformational change. Binding studies by equilibrium dialysis indicate the presence of 50 binding sites in the protein and binding constant of 3-0 X 10(3).

Alpha-Globulins↗