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  • 1
    Electronic Resource
    Electronic Resource
    Spin probe clustering in human erythrocyte ghosts (1985)
    Springer
    The journal of membrane biology 84 (1985), S. 81-95 
    Details
    ISSN: 1432-1424
    Keywords: erythrocyte ghosts ; spin probe ; radical interactions ; lipid domains ; fluidity ; electron spin resonance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary A model has been developed for 5-nitroxide stearate, I(12,3), distribution in human erythrocyte ghosts which accurately predicts ESR spectral alterations observed with increased probe/total lipid (P/L) at 37°C. This spin probe occupies a class of high-affinity, noninteracting sites at low loading. Saturation occurs with increasing probe concentration, and, at higher loading, the probe inserts itself at initially dilute sites to form membranebound clusters of variable size. No ‘low’ probe remains at high P/L where all I(12,3) clusters in a ‘concentrated’ phase. This model allows determination of the dilute/clustered probe ratio, and shows that I(12,3) segregates in erythrocytes at what might otherwise be considered low P/L (e.g., 1/359). These findings validate the earlier use of empirical parameters to estimate probe sequestration in biological membranes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871650
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  • 2
    Electronic Resource
    Electronic Resource
    Fatty-acid spin probe interactions with erythrocyte ghosts and liposomes prepared from erythrocyte ghosts (1989)
    Springer
    The journal of membrane biology 111 (1989), S. 155-168 
    Details
    ISSN: 1432-1424
    Keywords: erythrocyte ghosts ; liposomes ; radical interactions ; protein ; lipid domains ; fluidity ; electron spin resonance ; spin probes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary A model for the binding of 5-nitroxide stearate, I(12,3). to human erythrocyte ghosts was developed by comparing spin probe interactions with ghosts and liposomes prepared from ghosts. At low probe/lipid (P/L〈1/2500), I(12,3) binds to a similar class of high-affinity, noninteracting sites in both ghosts and liposomes, indicating that lipid moieties are responsible for probe uptake. Saturation occurs in both systems with increasing P/L, and, at higher loading (e.g., P/L=1/360 for ghosts and liposomes), the probe inserts itself at initially dilute sites to form a class of low-affinity sites consisting of clusters of variable size. At still higher P/L ranges (〉1/100), much increased probe uptake was observed in ghosts than in liposomes, which was attributed to another class of low-affinity sites, representing nonspecific interactions of I(12,3) with membrane proteins. The nature of the spectral components and ultrafiltration experiments with ghosts labeled at high P/L indicate that both ‘dilute’ and ‘clustered’ I(12,3) are due to membrane-incorporated probe.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871779
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  • 3
    Electronic Resource
    Electronic Resource
    Thermotropic lipid phase separations in human erythrocyte ghosts and cholesterol-enriched rat liver plasma membranes (1984)
    Springer
    The journal of membrane biology 79 (1984), S. 75-86 
    Details
    ISSN: 1432-1424
    Keywords: erythrocyte ghosts ; liver plasma membranes ; spin probe ; cholesterol ; lipid phase separation ; lipid domains ; hemolysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Electron spin resonance (ESR) studies of human erythrocyte ghosts labeled with 5-nitroxide stearate, I(12,3), indicate that a temperature-dependent lipid phase separation occurs with a high onset at 38°C. Cooling below 38°C induces I(12,3) clustering. Similar phase separations were previously identified in human platelet and cholesterol-loaded [cholesterol/phospholipid molar ratio (C/P)=0.85] rat liver plasma membranes [L.M. Gordon et al., 1983;J. Membrane Biol. 76; 139–149]; these were attributed to redistribution of endogenous lipid components such that I(12,3) is excluded from cholesterol-rich domains and tends to reside in cholesterol-poor domains. Further enrichment of rat liver plasma membranes to C/P ratios of 0.94–0.98 creates an “artificial” system equivalent to human erythrocyte ghosts (C/P=0.90), using such criteria as probe flexibility, temperature dependent I(12,3) clustering; and polarity of the probe environment. Consequently, cholesterol-rich and-poor domains probably exist in both erythrocyte ghosts and high cholesterol liver membranes at physiologic temperatures. The temperature dependence of cold-induced hypertonic lysis of intact human erythrocytes was examined by incubating cells in 0.9m sucrose for 10 min at 1°C intervals between 9 and 46°C (Stage 1), and then subjecting them to 0°C for 10 min (Stage 2). Plots of released hemoglobin are approx. sigmoidal, with no lysis below 18°C and maximal lysis above 40°C. The protective effect of low temperatures during Stage 1 may be due to the formation of cholesterol-rich domains that alter the bilayer distribution and/or conformation of critical membrane-associated proteins.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868528
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  • 4
    Electronic Resource
    Electronic Resource
    Spin-label studies on rat liver and heart plasma membranes: Do probe-probe interactions interfere with the measurement of membrane properties? (1977)
    Springer
    The journal of membrane biology 31 (1977), S. 131-169 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The structures of purified rat liver and heart plasma membranes were studied with the 5-nitroxide stearic acid spin probe,I(12, 3). ESR spectra were recorded with a 50 gauss field sweep, and also with a new technique which “expands” the spectrum by (1) recording pairs of adjoining peaks with a smaller field sweep and (2) superposing the common peaks. The hyperfine splittings measured from the “expanded” spectra were significantly more precise than those obtained from the “unexpanded” spectra. Both procedures were used to study the effects of variousI(12,3) prove concentrations on the spectra of liver and heart membranes, as well as the effects of temperature and CaCl2 additions on the spectra of liver membranes, and revealed the following: The polarity-corrected order parameters of liver (31°) and heart (22°) membranes were found to be independent of the probe concentration, if experimentally-determined lowI(12,3)/lipid ratios were employed. The absence of obvious radical-interaction broadening in the unexpanded spectra indicated that “intrinsic” membrane properties may be measured at these low probe/lipid ratios. Here, “intrinsic” properties are defined as those which are measured when probe-probe interactions are negligible, and do not refer to membrane behavior in the absence of a perturbing spin label. At higherI(12,3)/lipid ratios, the order parameters of liver and heart membranes were found to substantially decrease with increasing probe concentration. The increase in the “apparent” fluidity of both membrane systems is attributed to enhanced radical interactions; however, an examination of these spectra (without reference to “low” probe concentration spectra) might incorrectly suggest that radical interactions were absent. For the membrane concentrations employed in these studies, the presence of “liquid-lines” (or “fluid components”) in the unexpanded ESR spectra was a convenient marker of high probe concentrations. A thermotropic phase separation was observed in liver membranes between 19° and 28°. Addition of CaCl2 to liver plasma membrane [labelled with “low”I(12,3) concentrations] increased the rigidity of the membrane at 31° and 37°, without inducing a segregation of the probe in the bilayer. Previously reported data are discussed in relation to these results, and suggested minimal criteria for performing membrane spin label studies are included.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869402
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  • 5
    Electronic Resource
    Electronic Resource
    Effects of calcium, lanthanum, and temperature on the fluidity of spin-labeled human platelets (1980)
    Springer
    The journal of membrane biology 52 (1980), S. 201-219 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Previous platelet studies have shown that calcium plays important roles in stimulus-secretion coupling, aggregation, and other membrane-associated functions. In addition, lanthanum induces platelet aggregation and the platelet release reaction and also influences platelet responsiveness to various stimuli. The spin-label results presented here suggest that one mechanism through which calcium and lanthanum mediate their effects on platelet functions may be by decreasing the lipid fluidity of the surface membrane. The structure of platelet membrane lipids was examined with the spin-label method. Washed human platelets were labeled with the 5-, 12- and 16-nitroxide stearic acid spin probes. Order parameters which measure the fluidity of the lipid environment of the incorporated probe may be calculated from the electron spin resonance (ESR) spectra of 5-nitroxide stearate [I(12,3)]-labeled cells. Evidence is presented which indicates that these spectra principally reflect properties of the platelet surface membrane lipids. The membrane fluidity increased with temperature for the range 17 to 37 °C. Either calcium or lanthanum additions to intact cells increased the rigidity of the platelet membranes at 37 °C, although the La3+ effect was larger and occurred at lower concentrations than that of Ca2+. For example, addition of 1mm La3+ or 4mm Ca2+ increased the order parameter of I(12,3)-labeled platelets by 4.3±1.7% or 2.1±0.5%. Preliminary studies conducted on purified platelet plasma membranes labeled with I(12,3) indicated that 1mm LaCl3 or 4mm CaCl2 additions similarly decreased the lipid fluidity at 37 °C. The above cation-induced effects on the fluidity of whole platelets were reversed by the use of the divalent cation-chelating agent ethylene glycol-bis-(β-aminoethyl ether)-N,N′-tetra-acetic acid (EGTA). Lastly, lanthanum (0.2–1mm) caused rapid aggregation of platelets which were suspended in a 50-mm Tris buffer pH 7.4 that did not contain adenosine.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869190
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  • 6
    Electronic Resource
    Electronic Resource
    Thermotropic lipid phase separations in human platelet and rat liver plasma membranes (1983)
    Springer
    The journal of membrane biology 76 (1983), S. 139-149 
    Details
    ISSN: 1432-1424
    Keywords: platelet plasma membranes ; liver plasma membranes ; spin probe ; cholesterol ; lipid phase separation ; platelet acid phosphatase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Electron spin resonance (ESR) studies were conducted on human platelet plasma membranes using 5-nitroxide stearate, I(12,3). The polarity-corrected order parameterS and polarity-uncorrected order parametersS(T ‖) andS(T ⊥) were independent of probe concentration at low I(12,3)/membrane protein ratios. At higher ratios,S andS(T ⊥) decreased with increasing probe concentration whileS(T ‖) remained unchanged. This is the result of enhanced radical interactions due to probe clustering. A lipid phase separation occurs in platelet membranes that segregates I(12,3) for temperatures less than 37°C. As Arrhenius plots of platelet acid phosphatase activity exhibit a break at 35 to 36°C, this enzyme activity may be influenced by the above phase separation. Similar experiments were performed on native [cholesterol/phospholipid ratio (C/P)=0.71] and cholesterol-enriched [C/P=0.85] rat liver plasma membranes. At 36°C, cholesterol loading reduces I(12,3) flexibility and decreases the probe ratio at which radical interactions are apparent. The latter effects are attributed to the formation of cholesterol-rich lipid domains, and to the inability of I(12,3) to partition into these domains because of steric hinderance. Cholesterol enrichment increases both the high temperature onset of the phase separation occurring in liver membranes from 28° to 37°C and the percentage of probe-excluding, cholesterolrich lipid domains at elevated temperatures. A model is discussed attributing the lipid phase separation in native liver plasma membranes to cholesterol-rich and-poor domains. As I(12,3) behaves similarly in cholesterol-enriched liver and human platelet plasma membranes, cholesterol-rich and-poor domains probably exist in both systems at physiologic temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02000614
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  • 7
    Electronic Resource
    Electronic Resource
    The selective effects of charged local anaesthetics on the glucagon- and fluoride-stimulated adenylate cyclase activity of rat-liver plasma membranes (1980)
    New York, N.Y. : Wiley-Blackwell
    Journal of Supramolecular Structure 14 (1980), S. 21-32 
    Details
    ISSN: 0091-7419
    Keywords: glucagon ; adenylate cyclase ; anaesthetics ; membrane bilayer fluidity ; Life Sciences ; Molecular Cell Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: The cationic local anaesthetics carbocaine and unpercaine were found to increase the fluoride-stimulated adenylate cyclase up to a maximum level; above this maximum level further increases in drug concentration inhibited the enzyme. At concentrations where this activity was stimulated, a fatty acid spin label detected an increase in bilayer fluidity, which, it is suggested, is responsible for the activation of the enzyme. A solubilized enzyme was unaffected by the drugs, a finding consistent with this proposal.These cationic drugs began to inhibit the glucagon-stimulated activity at concentrations where they activated the fluoride-stimulated activity. It is suggested that this is due to their effect on the coupling interaction between the receptor and catalytic unit.The anionic drugs, phenobarbital, pentobarbital, and salicylic acid, all inhibited the fluoride-stimulated enzyme. This may be due in part to a direct effect on the protein and in part to the interaction of the drugs with the bilayer. The drugs had small inhibitory effects on the lubrol-solubilized enzyme.The glucagon-stimulated enzyme was initially inhibited by the anionic drugs at low concentrations, then activated, and finally inhibited with increasing drug concentration. The reasons for such changes are complex, but there was no evidence from electron spin resonance studies to suggest that the elevations in activity were due to increases in bilayer fluidity.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jss.400140104
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  • 8
    Electronic Resource
    Electronic Resource
    Conformational mapping of a viral fusion peptide in structure-promoting solvents using circular dichroism and electrospray mass spectrometry (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 33 (1998), S. 38-49 
    Details
    ISSN: 0887-3585
    Keywords: MS/MS electrospray mass spectrometry ; CD ; human immunodeficiency virus (HIV) ; glycoprotein 41,000 (gp41) ; N-terminal domain ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The N-terminal domain of human immunodeficiency virus (HIV)-1 glycoprotein 41,000 (FP; residues 1-23; NH2-AVGIGALFLGFLGAAGSTMGARS-CONH2) is involved in the fusion and cytolytic processes underlying viral-cell infection. Here, we use circular dichroism (CD) spectroscopy, along with electrospray ionization (ESI) mass spectrometry and tandem (MS/MS) mass spectrometry during the course of hydrogen/deuterium exchange, to probe the local conformations of this synthetic peptide in two membrane mimics. Since amino acids that participate in defined secondary structure (i.e., α-helix or β-sheet) exchange amido hydrogens more slowly than residues in random structures, deuterium exchange was combined with CD spectroscopy to map conformations to specific residues. For FP suspended in the highly structure-promoting solvent hexafluoroisopropanol (HFIP), CD spectra indicated high α-helix and disordered structures, whereas ESI and MS/MS mass spectrometry indicated that residues 5-15 were α-helical and 16-23 were disordered. For FP suspended in the less structure-promoting solvent trifluoroethanol (TFE), CD spectra showed lower α-helix, with ESI and MS/MS mass spectrometry indicating that only residues 9-15 participated in the α-helix. These results compare favorably with previous two-dimensional nuclear magnetic resonance studies on the same peptide. Proteins Suppl. 2:38-49, 1998. © 1998 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Spin label studies on rat liver and heart plasma membranes: Effects of temperature, calcium, and lanthanum on membrane fluidity (1978)
    New York, N.Y. : Wiley-Blackwell
    Journal of Supramolecular Structure 9 (1978), S. 299-326 
    Details
    ISSN: 0091-7419
    Keywords: lanthanum ; calcium ; lipid phase separation ; lipid clusters ; spin label method ; membrane fluidity ; temperature ; Life Sciences ; Molecular Cell Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: The structures of rat liver and heart plasma membranes were studied with the 5-nitroxide stearic acid spin probe, I(1 2,3). The polarity-corrected order parameters (S) of liver and heart plasma membranes were independent of probe concentration only if experimentally determined low I(1 2,3)/lipid ratios were employed. At higher probe/lipid ratios, the order parameters of both membrane systems decreased with increasing probe concentration, and these effects were attributed to enhanced nitroxide radical interactions. Examination of the temperature dependence of approximate and polarity-corrected order parameters indicated that lipid phase separations occur in liver (between 19° and 28°C) and heart (between 21° and 32°C) plasma membranes. The possibility that a wide variety of membrane-associated functions may be influenced by these thermotropic phase separations is considered.Addition of 3.9 mM CaCl2 to I(1 2,3)-labeled liver plasma membrane decreased the fluidity as indicated by a 5% increase in S at 37°C. Similarly, titrating I(1 2,3)-labeled heart plasma membranes with either CaCl2 or LaCl3 decreased the lipid fluidity at 37°C, although the magnitude of the La3+ effect was larger and occurred at lower concentrations than that induced by Ca2+; addition of 0.2 mM La3+ or 3.2 mM Ca2+ increased S by approximately 7% and 5%, respectively. The above cation effects reflected only alterations in the membrane fluidity and were not due to changes in probe-probe interactions. Ca2+ and La3+ at these concentrations decrease the activities of such plasma membrane enzymes as Na+, K+-ATPase and adenylyl cyclase, and it is suggested that the inhibition of these enzymes may be due in part to cation-mediated decreases in the lipid fluidity.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jss.400090303
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