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Biomedical subjects

R Pal

Publications and source records attributed to R Pal.

At least 127 records · Page 7Linked to original sources
PubMed1983

Lipid and protein contributions to the membrane surface potential of vesicular stomatitis virus probed by a fluorescent pH indicator, 4-heptadecyl-7-hydroxycoumarin.

The surface potential of membranes of vesicular stomatitis virus and liposomes was determined by shift of ionization over a wide pH range of the membrane-inserted fluorophore, 4-heptadecyl-7-hydroxycoumarin. Incorporation into sonicated vesicles of negatively charged phosphatidylserine markedly increased the surface potential of uncharged phosphatidylcholine, but no significant effect on surface potential was produced by polar but uncharged glucocerebroside incorporated in phosphatidylcholine vesicles. The membrane of vesicular stomatitis virus was found to have a moderately high surface potential. Contributing to this viral membrane surface potential were glycoprotein spikes and phospholipid headgroups as determined by lowered charge after treatment of intact virions with thermolysin to remove glycoprotein or phospholipase C to remove phospholipid headgroups. The role of viral glycoprotein was confirmed by demonstrating increased surface charge of vesicles reconstituted with both viral glycoprotein and lipids compared with vesicles reconstituted with viral lipids alone. An unexpected finding was the large contribution to surface potential of cholesterol present in viral membrane. Increasing cholesterol concentration in virions by interaction with cholesterol-complexed serum lipoproteins resulted in a marked decrease in surface potential, whereas 75% depletion of virion cholesterol by interaction with sphingomyelin-complexed serum lipoproteins resulted in a significant increase in virion membrane surface potential. Although removal of glycoprotein spikes or depletion of cholesterol causes reduction in infectivity of vesicular stomatitis virus, no direct correlation could be found between alteration in surface charge and infectivity.

Hydrogen-Ion Concentration↗
PubMed1982

Thiomethylation and thiohydroxylation--a new pathway of metabolism of heterocyclic compounds.

1. G.l.c.--mass spectral analysis of t.l.c. fractions of urine samples of patients treated with 5-(2-chloroethyl)-4-methylthiazole (clomethiazole), has revealed two minor metabolites, each with two sulphur atoms. 2. Their structures were found to be 2-methylthio-clomethiazole and 5-acetyl-4-methyl-2-mercapto-thiazole, formed by thiomethylation and thiohydroxylation, respectively, of the original compound. 3. The structures of six other minor metabolites resulting from side-chain degradation have been elucidated. 4. The occurrence of metabolites with substituents at position 2 of the heterocyclic nucleus is assumed to be initiated by oxidative attack at the nitrogen, followed by nucleophilic substitution in position 2.

Chemical Phenomena↗
PubMed1981

Pardaxin, a hydrophobic toxin of the Red Sea flatfish, disassembles the intact membrane of vesicular stomatitis virus.

Reaction of vesicular stomatitis virus with pardaxin, the hydrophobic toxin of the Red Sea flatfish, resulted in a profound morphological change of many virions and dissociation of their membrane and nucleocapsid into components readily separable by density gradient centrifugation. The basic matrix protein and acidic pardaxin segregated largely with the high density nucleocapsid. The dissociated virion membrane formed lipoprotein vesicles which retained glycoprotein spikes and a certain amount of N protein but no appreciable amounts of other nucleocapsid proteins and little if any RNA. Iodination of the tyrosine residue of the glycoprotein tail fragment provided supporting evidence that the COOH terminus of the glycoprotein extends beyond the inner layer of the membrane into the interior of the virion. These data indicate that pardaxin may serve as a probe for studying the organization of viral membranes, and, hopefully, other biological membranes.

Animals↗
PubMed1981

Fluorescence studies of dipalmitoylphosphatidylcholine vesicles reconstituted with the glycoprotein of vesicular stomatitis virus.

The vesicular stomatitis virus glycoprotein (G) was reconstituted into dipalmitoylphosphatidylcholine (DPPC) vesicles by detergent dialysis. The DPPC gel to liquid-crystalline phase transition of the DPPC-G protein vesicles was monitored by the fluorescence anisotrophy of trans-paranaric acid, 16-(9-anthroyloxy)palmitoylglucocerebroside, 1,6-diphenyl-1,3,5-hexatriene, and 4-heptadecyl-7-hydroxycoumarin. The DPPC transition temperature measured by all four fluorescent probes was lowered in the presence of the G protein and the DPPC gel state was disordered by the G protein as evidenced by a decreased fluorescence anisotropy for all four probes below the phase-transition temperature. A possible ordering of the DPPC liquid-crystalline state by the G protein was indicated by an increased anisotropy of trans-paranaric acid and 16-(9-anthroyloxy)palmitoylglucocerebroside in the liquid-crystalline state of DPPC-G protein vesicles. The G protein in addition affected the ionization of the 4-heptadecyl-7-hydroxycoumarin in lipid vesicles, increasing the apparent pK of the probe from 9.05 to 9.45.

Diphenylhexatriene↗
PubMed1981

Fluorescence anisotropy of a fatty acid covalently linked in vivo to the glycoprotein of vesicular stomatitis virus.

The covalently-attached fatty acid of the membrane glycoprotein (G) of vesicular stomatitis virus was fluorescently labeled biologically by isolating vesicular stomatitis virus from infected baby hamster kidney clone 21 cells that had been grown in the presence of 16(9-anthroyloxy)palmitate. The fluorescent labeling was specific for the G protein; the other viral membrane protein, the matrix (M) protein, was not labeled. Steady state fluorescence anisotropy of the 16(9-anthroyloxy)palmitate-labeled G protein reconstituted into dipalmitoylphosphatidylcholine vesicles indicated that the fatty acid attached to G protein is located in a dipalmitoylphosphatidylcholine domain that does not undergo the gel to liquid-crystalline phase transition.

Animals↗
PubMed1981

Depletion and exchange of cholesterol from the membrane of vesicular stomatitis virus by interaction with serum lipoproteins or poly(vinylpyrrolidone) complexed with bovine serum albumin.

Cholesterol was depleted from the membrane of vesicular stomatitis virus by exposing virion suspensions to serum lipoproteins enriched with phospholipids. Unlike the reaction of virions with phospholipid vesicle, nonspecific adherence of lipoproteins and exogenous lipids to the envelope of the virus was found to be minimal. The extent of cholesterol depletion was dependent upon the type of phospholipid complexed with interacting lipoprotein; sphingomyelin and dipalmitoyllecithin were found to be highly effective depleters of cholesterol compared to egg phosphatidylcholine, phosphatidylethanolamine, or phosphatidylserine. Similar depletion of cholesterol from the virion membrane was also observed when vesicular stomatitis virus was exposed to a complex of poly(vinylpyrrolidone) and bovine serum albumin coated with egg phosphatidylcholine or dioleoylphosphatidylcholine. Cholesterol depletion was found to alter the morphology but not the membrane integrity of the virus. Directly correlated with depletion of cholesterol was a substantial loss in the anisotropy of the viral membrane as determined by fluorescence depolarization of the lipophilic probe 1,6-diphenyl-1,3,5-hexatriene. Interaction with poly(vinylpyrrolidone) complexed with albumin, phosphatidylcholine, and cholesterol resulted in exchange of cholesterol from the virion membrane which following biphasic kinetics with a rapid and a slow phase; these data indicate that 75-85% of viral membrane cholesterol is present in the outer monolayer, and 15-25% is located in the inner monolayer. Depletion of cholesterol from the virion membrane resulted in a significant drop in the infectivity of the virus as measured by plating efficiency on L-cell monolayers. Such an effect was not observed when virion cholesterol was exchanged without net reduction in the concentration of viral membrane cholesterol. Part of the loss in infectivity following depletion of cholesterol could be restored by reincorporation of cholesterol in the membrane, thus demonstrating that membrane cholesterol partly contributes to the infectivity of vesicular stomatitis virus.

Animals↗
PubMed1981

Transcription of vesicular stomatitis virus activated by pardaxin, a fish toxin that permeabilizes the virion membrane.

The toxic protein, Pardaxin, of the Red Sea flatfish Pardachirus marmoratus readily induced transcription of vesicular stomatitis virus by making the virion membrane permeable to nucleoside triphosphates in the absence of nonionic detergents. Virion transcription was activated over a wide range of Pardaxin concentrations, but at optimal concentrations, the rate of transcription exceeded that induced by Triton X-100. The inhibitory effect of M protein was manifested for both Pardaxin-induced and Triton-induced transcription at high concentrations of vesicular stomatitis virions; however, unlike the Triton-induced reaction, the inhibitory effect of M protein was not reversed by polyglutamic acid added to the Pardaxin-induced transcription reaction. We propose that activation of virion transcription by Pardaxin resembles more closely intracellular transcription initiated by virion penetration than does detergent-activated transcription of vesicular stomatitis virus.

DNA-Directed RNA Polymerases↗
PubMed1980

Alteration of the membrane lipid composition and infectivity of vesicular stomatitis virus by growth in a Chinese hamster ovary cell sterol mutant and in lipid-supplemented baby hamster kidney clone 21 cells.

The cholesterol and phospholipid composition of the membrane of vesicular stomatitis (VS) virus was altered by growth in a sterol auxotroph Chinese hamster ovary (CHO MI) host cell and by infection of CHO MI and baby hamster kidney (BHK)-21 cells supplemented with fatty acids and dimethylethanolamine. VS virus released from infected CHO MI sterol auxotroph cells grown in delipidated serum had a 50% lower ratio of cholesterol to phospholipid and an 80% drop in infectivity measured by plaque formation on L-929 cells compared with VS virus released from infected CHO MI cells grown in fetal calf serum. When VS virus was harvested from infected BHK-21 cells fed the choline analogue dimethylethanolamine, 29% of the membrane phospholipids were phosphatidyldimethylethanolamine (PDME); 87% of the PDME was located in the external monolayer of the virus membrane as determined by phospholipase C hydrolysis. Exogenous fatty acids added to the medium of cells infected with VS virus comprised up to 30% of the fatty acyl chains of the viral glycerophospholipids. The presence of PDME or unusual fatty acyl chains in the viral membrane had no effect on viral infectivity. These data indicate that the lipid composition of the VS virus membrane is determined primarily by the lipids available in the host cell and that only cholesterol content affects the biological activity of the virus membrane.

Animals↗
PubMed1980

Thermotropic behavior of dipalmitoylphosphatidylcholine vesicles reconstituted with the glycoprotein of vesicular stomatitis virus.

The vesicular stomatitis virus glycoprotein reconstituted into dipalmitoylphosphatidylcholine (DPPC) vesicles exerts a profound effect upon the DPPC gel to liquid-crystalline phase transition. The glycoprotein was reconstituted into DPPC vesicles by octyl glucoside dialysis. The gel to liquid-crystalline phase transition of these vesicles was monitored by differential scanning calorimetry. Vesicles formed in the absence of glycoprotein (600--2100-A diameter) underwent the phase transition at 41.0 degrees C and had an associated enthalpy change of 8.0 +/- 1.6 kcal/mol. Increasing the mole ratio of glycoprotein to DPPC in the vesicles to 0.15 mol % reduced both the transition temperature and the transition enthalpy change. The enthalpy change as a function of the mole percent glycoprotein could be fit to a straight line by a least-squares procedure. Extrapolation of the results to the glycoprotein concentration where the enthalpy change was zero indicated one glycoprotein molecule bound 270 +/- 150 molecules of DPPC.

Calorimetry, Differential Scanning↗