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Biomedical subjects

I W Levin

Publications and source records attributed to I W Levin.

At least 55 records · Page 3Linked to original sources
PubMed1986

Effects of cyclosporine A on biomembranes. Vibrational spectroscopic, calorimetric and hemolysis studies.

Cyclosporine A (CSA)-dipalmitoylphosphatidylcholine (DPPC) interactions were investigated using scanning calorimetry, infrared spectroscopy, and Raman spectroscopy. CSA reduced both the temperature and the maximum heat capacity of the lipid bilayer gel-to-liquid crystalline phase transition; the relationship between the shift in transition temperature and CSA concentration indicates that the peptide does not partition ideally between DPPC gel and liquid crystalline phases. This nonideality can be accounted for by excluded volume interactions between peptide molecules. CSA exhibited a similar but much more pronounced effect on the pretransition; at concentrations of 1 mol % CSA the amplitude of the pretransition was less than 20% of its value in the pure lipid. Raman spectroscopy confirmed that the effects of CSA on the phase transitions are not accompanied by major structural alterations in either the lipid headgroup or acyl chain regions at temperatures away from the phase changes. Both infrared and Raman spectroscopic results demonstrated that CSA in the lipid bilayer exists largely in a beta-turn conformation, as expected from single crystal x-ray data; the lipid phase transition does not induce structural alterations in CSA. Although the polypeptide significantly affects DPPC model membrane bilayers, CSA neither inhibited hypotonic hemolysis nor caused erythrocyte hemolysis, in contrast to many chemical agents that are believed to act through membrane-mediated pathways. Thus, agents, such as CSA, that perturb phospholipid phase transitions do not necessarily cause functional changes in cell membranes.

Calorimetry, Differential Scanning↗
PubMed1985

A Raman spectroscopic study on the effect of cholesterol on lipid packing in diether phosphatidylcholine bilayer dispersions.

For assessing lipid-sterol packing characteristics in model membrane systems, the vibrational Raman spectra of 1,2-di-O-hexadecyl-sn-glycero-3-phosphocholine (DHPC) multilamellar dispersions containing 18 mol% cholesterol were examined. The thermotropic behavior of the pure diether- and cholesterol-containing bilayers were studied in both the C-H stretching (2800-3100 cm-1) and C-C stretching (1000-1200 cm-1) mode regions, spectral intervals reflecting intermolecular and intramolecular order/disorder characteristics. Pure DHPC bilayers exhibit the pretransition and gel to liquid-crystalline phase transition temperatures at approx. 31 and 42.8 degrees C, respectively. In contrast to the temperature behavior of dipalmitoylphosphatidylcholine-cholesterol bilayers in which the primary phase transition Tm, is simply broadened, Tm is increased to approx. 49.6 degrees C in the DHPC (diether PC) liposomes containing 18 mol% cholesterol. As in the saturated chain diacyl-cholesterol bilayer systems, the sterol disorders the DHPC gel phase and eliminates the pretransition, while ordering the liquid-crystalline phase. Pure diether liposomes exhibit a headgroup dehydration effect as the multilamellar dispersions are cycled slowly over a temperature range including the gel and liquid-crystalline forms. That is, on multiple passages through the phase transitions, both the gel and liquid-crystalline bilayer forms assume an increased hydrocarbon chain order. In the cholesterol-containing diether bilayers, only the disordered intra- and interchain states are formed.

Chemical Phenomena↗
PubMed1985

Two types of hydrocarbon chain interdigitation in sphingomyelin bilayers.

Vibrational Raman spectroscopic experiments have been performed as a function of temperature on aqueous dispersions of synthetic DL-erythro-N-lignoceroylsphingosylphosphocholine [C(24):SPM], a racemic mixture of two highly asymmetric hydrocarbon chain length sphingomyelins. Raman spectral peak-height intensity ratios of vibrational transitions in the C-H stretching-mode region show that the C(24):SPM-H2O system undergoes two thermal phase transitions centered at 48.5 and 54.5 degrees C. Vibrational data for fully hydrated C(24):SPM are compared to those of highly asymmetric phosphatidylcholine dispersions. The Raman data are consistent with the plausible model that the lower temperature transition can be ascribed to the conversion of a mixed interdigitated gel state (gel II) to a partially interdigitated gel state (gel I) and that the higher temperature transition corresponds to a gel I----liquid-crystalline phase transition. The observation of a mixed interdigitated gel state (gel II) at temperatures below 48.5 degrees C implies that biological membranes may have lipid domains in which some of the lipid hydrocarbon chains penetrate completely across the entire hydrocarbon width of the lipid bilayer.

Kinetics↗
PubMed1985

Secondary structure of endocrine amyloid: infrared spectroscopy of medullary carcinoma of the thyroid.

Infrared spectroscopic characteristics of deparaffinized tissue sections of the amyloid produced by medullary carcinoma of the thyroid confirm the presence of both beta-sheet and disordered conformations within the deposits. No evidence for alpha-helical structures is found. Amyloid produced by medullary carcinoma of the thyroid thus possesses secondary structural characteristics similar to amyloid of immunoglobulin origin. Infrared spectra were obtained directly from deparaffinized tissue sections, assuring that the chemical structure of amyloid in the recorded spectrum corresponds to that seen microscopically. This structure may or may not correspond to that in vivo, since fixation and dehydration may alter protein secondary structure.

Amyloid↗
PubMed1984

Raman spectroscopic study of an interdigitated lipid bilayer. Dipalmitoylphosphatidylcholine dispersed in glycerol.

Dipalmitoylphosphatidylcholine (DPPC) dispersed in perdeuterated glycerol was investigated in order to determine the effects on the Raman spectra of hydrocarbon chain interdigitation in gel-phase lipid bilayers. Interdigitated DPPC bilayers formed from glycerol dispersions in the gel phase showed a decrease in the peak height intensity I2850/I2880 ratio, for the symmetric and asymmetric methylene CH stretching modes, respectively, as compared to non-interdigitated DPPC/water gel-phase dispersions. The decrease in this spectral ratio is interpreted as an increase in chain-chain lateral interactions. Spectra recorded in the 700-740 cm-1 CN stretching mode region, the 1000-1200 cm-1 C-C stretching mode region and the 1700-1800 cm-1 C = 0 stretching mode region were identical for both the interdigitated and non-interdigitated hydrocarbon chain systems. At low temperatures the Raman peak height intensity ratios I2935/I2880 were identical for the DPPC/glycerol and DPPC/water dispersions, indicating that this specific index for monitoring bilayer behavior is insensitive to acyl chain interdigitation. The increase, however, in the change of this index at the gel-liquid crystalline phase transition temperature for the DPPC/glycerol dispersions implies a larger entropy of transition in comparison to the non-interdigitated DPPC/water bilayer system.

Glycerol↗
PubMed1984

Effects of anesthetic and nonanesthetic steroids on dipalmitoylphosphatidylcholine liposomes: a calorimetric and Raman spectroscopic investigation.

The effects of anesthetic and nonanesthetic steroids on dipalmitoylphosphatidylcholine liposomes were studied by use of high sensitivity scanning calorimetry and Raman spectroscopy. Calorimetric measurements indicated that both anesthetic and nonanesthetic steroids depressed and broadened the gel to liquid-crystalline phase transition. There was no correlation between the perturbations by the steroids on the primary gel to liquid-crystalline phase transition temperature and anesthetic potency. The magnitudes of the steroid-induced transition broadening and lowering of the pretransition temperature, however, correlated well with anesthetic potency. This effect appeared to arise from the projection from the plane of the D ring of substituents at the C(17) position of the steroid nucleus. Raman spectroscopic measurements demonstrated that the steroid molecule is localized within the acyl region of the bilayer and that effects of the steroid do not extend to either the head-group or interface regions of the lamellae. The data are consistent with unitary hypotheses relating general anesthesia to lipid perturbations. For model systems, perturbations to the subtle structural and dynamical properties of the bilayer pretransition may provide a more sensitive marker than the main phase transition in assessing the significance of lipid mediation in inducing anesthetic action.

Anesthetics↗
PubMed1984

Membrane lipid response to clathrin coat protein determined by infrared spectroscopy. Possible involvement in coated vesicle formation.

Clathrin, the major structural protein associated with both coated pits and coated vesicles, has been implicated in the dynamics of various endocytotic processes. In an attempt to define the mechanisms involved in the transition from uncoated membranes to clathrin-coated pits and then to coated vesicles, we investigated by infrared spectroscopy the lipid perturbations arising from the interactions of the clathrin coat with the bilayers of intact membrane assemblies. A comparison of the lipid acyl chain symmetric methylene stretching modes at approximately 2850 cm-1 for isolated clathrin-coated vesicles, uncoated vesicles, and synaptic membranes at 21, 38, and 50 degrees C indicated that clathrin significantly increases the number of gauche chain conformers in the bilayer matrix of the coated vesicle system. The increase in lipid disorder at 21 degrees C, accompanying the observed 0.44-cm-1 frequency increase for coated vesicles compared to uncoated vesicles, is approximately equivalent to the intrachain disorder incurred in heating liquid crystalline dimyristoylphosphatidylcholine multilayers by approximately 10 degrees C. The implications of these results on coated vesicle formation are discussed.

Animals↗
PubMed1982

Infrared spectroscopic study of the secondary structure of melittin in water, 2-chloroethanol, and phospholipid bilayer dispersions.

The conformations of melittin, an amphipathic polypeptide consisting of 26 amino acid residues, and its hydrophobic (residues 1--19) and hydrophilic (residues 20--26) fragments were examined in various solvent systems, including H2O, 2H2O, 2-chloroethanol, and 1,2-dimyristoylphosphatidylcholine (DMPC) multilayers, by infrared spectroscopy. Water and 2-chloroethanol were used as reference solvents for characterizing the amide I and II vibrational frequencies of the polypeptide in systems reflecting unordered, beta-structure, or alpha-helical forms. In DMPC bilayer assemblies both melittin and its hydrophobic fragment F1 exhibit alpha-helical conformations. In contrast, infrared spectra for the hydrophilic F2 fragment are suggestive of a beta conformation with perhaps spectral contributions from random-coil configurations. The alpha-helical conformation of intact melittin in DMPC multilayer dispersions remains unchanged as the bilayer passes from the gel to liquid-crystalline state. For melittin-water solutions the infrared spectra monitor changes in population of specific conformations as the temperature is varied. Thus, for melittin concentrations in which tetramers are dominant high temperatures (31 degrees C) favor the alpha-helical form, while low temperatures (8 degrees C) lead to populations of both beta and alpha-helical structures. At lower melittin concentrations for which monomers persist, high temperatures favor an unordered polypeptide form, while low temperatures induce an alpha-helical conformation. Although peak-height intensity ratios AII/AI for the amide I and II regions are difficult to interpret rigorously, values of this parameter for aqueous solutions of melittin suggest a sensitivity to structural changes involving the aggregation properties of the polypeptide.

Bee Venoms↗
PubMed1982

Effect of water on the molecular structure of a phosphatidylcholine hydrate. Raman spectroscopic analysis of the phosphate, carbonyl and carbon-hydrogen stretching mode regions of 1,2-dipalmitoylphosphatidylcholine dihydrate.

The Raman spectra of 1,2-dipalmitoylphosphatidylcholine (DPPC) dihydrate crystals were examined in (a) the 1250 and 1080 cm-1 PO-2 antisymmetric and symmetric stretching mode regions, (b) the 1730 cm-1 carbonyl stretching mode region and (c) the 2800-3100 cm-1 C-H stretching mode interval. No evidence was observed for hydrogen bonding effects involving the nonester phosphate oxygen atoms. Spectra of the DPPC dihydrate crystal in the 1250 cm-1 region are compared to spectra of both anhydrous and successively hydrated systems and to spectra of crystalline glycerylphosphorylcholine. The splitting pattern in the 1240 to 1280 cm-1 interval for the DPPC dihydrate was interpreted in terms of the different bonding arrangements assumed by the PO-2 groups in the two molecule asymmetric unit of the eight molecule unit cell. An unusual triplet is observed in the carbonyl stretching mode region around 1730 cm-1. These features reflect differing bond environments, relative to the polar and hydrophobic regions of the bilayer, of the 1- and 2-chain carbonyl groups. Spectra for crystalline DPPC dihydrate in the 3000 cm-1 C-H stretching mode region suggest a hybrid chain packing lattice which is analogous to the packing arrangement determined for the isostructurally similar DMPC dihydrate species.

Glycerylphosphorylcholine↗
PubMed1982

Comparative effects of melittin and its hydrophobic and hydrophilic fragments on bilayer organization by Raman spectroscopy.

For bilayer systems consisting of 1,2-dimyristoyl phosphatidylcholine (DMPC) incubated with melittin, a polypeptide capable of integrating itself within the membrane, temperature profiles derived from Raman spectroscopic data indicate the existence of an immobilized lipid annulus surrounding the polypeptide. In particular, temperature profiles derived from C--H, C--D and C--C stretching mode parameters for 25:1, 14:1 and 10:1 lipid:protein mole ratios exhibit two order-disorder transitions. The primary (lower) gel to liquid crystalline phase transition is depressed when polypeptide concentration is increased. The concentration-independent higher temperature transition is associated with a fluidization of the immobilized boundary lipids present at the lipid-polypeptide interface within the bilayer. We estimate that five to seven lipids are involved in this discrete boundary layer around the inserted membrane component. The behavior of the intrinsic hydrophobic (residues 1-19) and of the extrinsic hydrophilic (residues 20-26) portions of melittin in the bilayer is compared with the properties of the intact polypeptide. We emphasize evidence that both intrinsic and extrinsic components immobilize lipids contiguous to the polypeptide.

Animals↗
PubMed1981

Evidence for acyl chain trans/gauche isomerization during the thermal pretransition of dipalmitoyl phosphatidylcholine bilayer dispersions.

In order to clarify, in dipalmitoyl phosphatidylcholine multilayers, the effect of the 34 degrees C thermal pretransition on the acyl chain intramolecular disordering process, Raman spectra of dipalmitoyl phosphatidylcholine gels at 20 and 34 degrees C were compared in the 1000--1200 cm-1 skeletal C-C stretching region. In addition to an overall intensity decrease associated with a change in chain packing characteristics, the growth of intensity in the 1080--1090 and 1122 cm-1 regions in the 34--20 degrees C) difference spectrum clearly indicates that the thermal pretransition is accompanied by an increase in the population of hydrocarbon chain gauche rotamers toward the center of the bilayer.

Isomerism↗
PubMed1980

Structural reorganizations in lipid bilayer systems: effect of hydration and sterol addition on Raman spectra of dipalmitoylphosphatidylcholine multilayers.

Vibrational Raman spectroscopy was used in investigate the conformational behavior of dipalmitoylphosphatidylcholine (DPPC) bilayers perturbed by cholesterol and water, two membrane components whose lipid interactions involve different regions of the bilayer matrix. Upon the addition of cholesterol, an intrinsic membrane constituent, to an anhydrous bilayer in concentrations varying from 7 to 30 mol %, modifications in lateral chain interactions were observed by monitoring spectral changes in the methylene C-H stretching and the CH2 deformation regions. The perturbation in the 1460-cm-1 region was not spectroscopically observed until after the addition of 7 mol % of the sterol. Although chain-chain interactions are altered, no additional trans/gauche isomerization is developed along the hydrocarbon chains. Water, a peripheral bilayer component, was added to the multilayer assembly in the hydration range of 0.3 to 4 molecules of water per lipid molecule. Vibrational spectra characteristic of motions in the head-group, interfacial, and acyl chain regions of the lipid bilayer were observed. These data indicate that hydration confers a mobility to the head-group, glycerol, and carbonyl moieties. Shifts in the CN symmetric and PO2-antisymmetric stretching modes, occurring on the addition of approximately four molecules of water, indicate a conformational rearrangement within the polar head group. After approximately four molecules of water are added to the DPPC system, the spectral features of the gel system [70% (w/w) water] indicate that not further head-group changes nor increases in either acyl chain trans/gauche or lattice disorder arise on further hydration.

Cholesterol↗
PubMed1980

Interaction of melittin with dimyristoyl phosphatidylcholine liposomes: evidence for boundary lipid by Raman spectroscopy.

The interaction of melittin, a polypeptide consisting of 26 amino acid residues, with dimyristoyl phosphatidylcholine bilayers was investigated by vibrational Raman spectroscopy. Spectral peak height intensity ratios, involving vibrational transitions in both the 3000 cm-1 acyl chain methylene carbon-hydrogen stretching mode region and the 1100 cm-1 acyl chain carbon-carbon skeletal stretching mode interval, served as temperature profile indices for monitoring the bilayer order-disorder processes. For a lipid : melittin molar ratio of 14 : 1 two order-disorder transitions were observed. In comparison to a gel to liquid crystalline phase transition of 22.5 degrees C for the pure lipid, the lower transition, exhibiting a 2 degree C width, is centered at 17 degrees C and is associated with a depression of the main lipid phase transition of dimyristoyl phosphatidylcholine. The second thermal transition, displaying a 7 degree C interval, occurs at approx. 29 degrees C and is associated with the melting behavior of approximately seven immobilized boundary lipids which surround the inserted hydrophobic segment of the polypeptide. For a lipid : melittin molar ratio of 10 : 1 two thermal transitions are also observed at 11 and 30 degrees C. As before, they represent, respectively, the main gel to liquid crystalline phase transition and the melting behavior of approximately four boundary lipids attached to melittin. From these data alternative schemes are suggested for disposing the immobilized lipids around the hydrophobic portion of the polypeptide within the bilayer.

Bee Venoms↗
PubMed1980

Molecular conformations of cerebrosides in bilayers determined by Raman spectroscopy.

Vibrational Raman spectra of the solid and gel phases of bovine brain cerebrosides and the component fractions, kerasin and phrenosin, provide conformational information for these glycosphingolipids in bilayer systems. The carbon-carbon stretching mode profiles (1,150-1,000 cm-1) indicate that at 22 degrees C the alkyl chains assume an almost all-trans arrangement. These spectral data, combined with those from the C-H stretching region (3,050-2,800 cm-1), show that phrenosin forms the most highly ordered polycrystalline solid and kerasin the most ordered gel phase. The conformation of the unsaturated, 24-carbon acyl chains is monitored independently by a skeletal stretching mode at 1,112 cm-1. The alkyl chains in the kerasin and phrenosin gels are sufficiently extended to allow interdigitation of the 24-carbon acyl chains across the midplane of the bilayer. The amide I vibrational mode occurs at a lower frequency in solid phrenosin than kerasin, a shift consistent with stronger hydrogen bounding. This band is broadened and shifted to higher frequencies, however, in the phrenosin gel phase. In both the solid and gel phases natural cerebroside exhibits a composite amide I mode. The disruptive effects on cerebroside chain packing and headgroup orientation arising from mixing with dimyristoyl phosphatidylcholine are examined. Vibrational data for cerebroside are also compared to those for ceramide, sphingosine, and distearoyl phosphatidylcholine structures. Spectral interpretations are discussed in terms of calorimetric and X-ray structural data.

Animals↗