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R Mendelsohn

Publications and source records attributed to R Mendelsohn.

At least 91 records · Page 5Linked to original sources
PubMed1989

Infrared spectroscopic investigations of pulmonary surfactant. Surface film transitions at the air-water interface and bulk phase thermotropism.

The molecular structure of the phospholipid component of intact pulmonary surfactant isolated from bovine lung lavage has been examined by Fourier transform infrared spectroscopy. Two different physical states of the surfactant were examined by means of different infrared spectroscopic sampling techniques. Transmission infrared experiments were used to study the surfactant in the bulk phase. In these experiments, the thermotropic behavior of the bulk surfactant was monitored by temperature-induced variations in the phospholipid acyl chain CH2 stretching frequencies. A broad phase transition (confirmed by differential scanning calorimetry) was noted with an onset temperature near 15 degrees C and a completion temperature near 42 degrees C. In addition to the bulk transmission experiments, external reflection infrared spectroscopy was used to examine surfactant films in situ at the air-water interface. As surface pressure was increased from 0 to 43 dyn/cm, a gradual and continuous decrease in the CH2 stretching frequency was noted for the surfactant. Thus, under surface pressures which correspond to large lung volumes in vivo, the surfactant acyl chains exist mostly in the ordered (trans) configuration. The frequency shift in the CH2 stretching mode is consistent with a continuous ordering of the acyl chains upon compression over the pressure range 0-43 dyn/cm, and implies that a weakly cooperative phase transition occurs in the hydrocarbon region of the surface film. The surface film transition is especially noted in the pressure-area curve of the surfactant and approximates in two dimensions the broad thermotropic phase transition of the bulk phase surfactant. Substantial differences were observed between the response to surface pressure changes of intact surfactant compared with the main surfactant phospholipid, 1,2-dipalmitoyl-sn--glycero-3-phosphocholine. The changes in response are attributed to the presence of additional surfactant components. The current work demonstrates the ability of infrared spectroscopy to obtain structural information on the surfactant in physical states that directly relate to those in vivo.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1987

Attenuated total reflectance Fourier transform infrared studies of the interaction of melittin, two fragments of melittin, and delta-hemolysin with phosphatidylcholines.

Attenuated total reflectance Fourier transform infrared spectroscopy (ATR FT-IR) has been used to monitor alterations in phospholipid organization in thin layers of 1,2-dipalmitoylphosphatidylcholine (DPPC) and 1-palmitoyl-2-oleoylphosphatidylcholine (POPC), induced by the membrane lytic peptide melittin, its fragments 1-15 (hydrophobic fragment) and 16-26 (hydrophilic fragment), and delta-hemolysin. In addition, the secondary structures of the peptides and the orientation of helical fragments were determined with respect to the bilayer. The insertion of melittin into POPC caused large perturbations in the order and increased rates of motion of the acyl chains, as monitored by the frequency and half-width of the symmetric CH2 stretching vibration near 2850 cm-1, as well as by the ATR dichroic ratio for this mode. Changes in DPPC organization were less and were consistent with peptide-induced static disordering (gauche rotamer formation) in the acyl chains. Melittin adopted primarily an alpha-helical secondary structure, although varying small proportions of beta and/or aggregated forms were noted. The helical segments were preferentially oriented perpendicular to the bilayer plane. Several modes of melittin/lipid interaction were considered in an attempt to semiquantitatively understand the observed dichroic ratios. By considering the peptide as a bent rigid rod, a plausible model for its lytic properties has been developed. The hydrophilic fragment in DPPC showed a secondary structure with little alpha-helix present. As judged by its effect on phospholipid acyl chain organizational parameters, the fragment did not penetrate the bilayer substantially. The hydrophobic fragment in DPPC gave amide I spectral patterns consistent with a mixture of predominantly beta-antiparallel pleated sheet with a smaller fraction of alpha-helix.(ABSTRACT TRUNCATED AT 250 WORDS)

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1987

Fourier transform infrared and differential scanning calorimetric studies of a surface-active material from rabbit lung.

A surface-active material with a chemical composition consistent with lung surfactant and with the ability to lower surface tension on a Wilhelmy balance to about 6 mN/m, has been isolated from rabbit pulmonary lavage. The thermotropic properties have been characterized with the techniques of Fourier transform infrared spectroscopy (FT-IR) and Differential Scanning Calorimetry (DSC). FT-IR melting curves were constructed from the temperature-dependence of the lipid CH2 symmetric stretching vibrational frequencies near 2850 cm-1. A broad gel-liquid crystal phase transition with an onset temperature of about 22 degrees C, and a completion temperature of about 38 degrees C was observed, with slight sample-to-sample variations in temperatures. A similar completion temperature was noted in DSC endotherms. Ca2+ (5-10 mM) increased the onset temperature of the lipid-melting event, and induced an ordering of surfactant and of its lipid extract at all temperatures studied. The effect on the lipids was suggestive of a Ca2+-induced phase separation caused by ion binding to phosphatidylglycerol and other acidic components. Evidence for a direct interaction between Ca2+ and the phosphate groups was suggested through small Ca2+-induced shifts in the 1090 cm-1 symmetric PO2 stretching frequency. Removal of most of the protein component from a 10:1 (lipid/protein, w/w) sample caused an ordering of the resultant lipid fractions. In contrast, removal of most of the protein component from a 20:1 sample resulted in no change in lipid order or thermotropic behavior. These observations are discussed in light of the roles played both by Ca2+ and protein in the spreading of surfactant. The power of FT-IR to acquire useful structural information from complex biological tissues is demonstrated.

Animals↗
PubMed1987

Thermal denaturation of globular proteins. Fourier transform-infrared studies of the amide III spectral region.

Fourier transform-infrared (FT-IR) spectra are reported for the amide III spectral region of the native and thermally denatured forms of chymotrypsinogen, ribonuclease, bovine serum albumin, and lysozyme. Chymotrypsinogen denatures into structures containing substantial contributions from beta-sheets, while lysozyme and bovine serum albumin show increased amounts of random-coil forms. The changes observed for ribonuclease are quite small. Bovine serum albumin shows at least six bands in the 1,260-1,320 cm-1 region which undergo large intensity changes upon thermal denaturation, and hence are assignable to alpha-helical amide III modes. The large number of observed bands suggests that slight variations in helical geometry, symmetry, or interactions result in changed amide III frequencies, so that simple correlations between narrow frequency ranges and secondary structures may not be applicable for this mode. A widened frequency range is suggested as diagnostic for helical structures.

Amides↗
PubMed1987

Unusual partitioning behavior of CaATPase in dipalmitoylphosphatidylethanolamine/dielaidoylphosphatidylcholine++ + mixtures.

CaATPase from rabbit sarcoplasmic reticulum has been isolated, purified, stripped of its native lipids, and reconstituted into binary lipid mixtures of dielaidoylphosphatidylcholine (DEPC) and dipalmitoylphosphatidylethanolamine (DPPE) or acyl-chain perdeuterated DPPE (DPPE-d62). The partitioning properties of the protein were determined from differential scanning calorimetry (DSC) and Fourier transform infrared (FT-IR) spectroscopy. Acyl-chain perdeuteration allows the separate determination of the order and melting characteristics of each lipid species with FT-IR. The binary lipid mixture has been shown to be phase separated in the gel state (Brauner, J. W., and R. Mendelsohn, 1986, Biochim. Biophys. Acta, 861:16-24). The solid phases present at low temperatures correspond to a pure DEPC phase and a mixed phase of DEPC/DPPE-d62. Insertion of protein at 37 degrees C leads to a domain of relatively protein-free DPPE-d62 and a phase containing both lipids plus CaATPase. We suggest that CaATPase selects a fixed composition (60% DEPC, 40% DPPE-d62) for its immediate environment. The composition of the lipid in the immediate vicinity of protein is largely independent of the initial DEPC/DPPE-d62 ratios in the reconstitution protocol. The relevance of these results to observations of discrete domains in native membranes is discussed.

Animals↗
PubMed1986

A comparison of differential scanning calorimetric and Fourier transform infrared spectroscopic determination of mixing behavior in binary phospholipid systems.

Fourier transform infrared (FT-IR) spectroscopy and differential scanning calorimetry (DSC) have been used to elucidate the phase behavior of two binary lipid mixtures, acyl chain perdeuterated 1,2-dipalmitoylphosphatidylethanolamine (DPPE-d62)/1,2-dielaidoylphosphatidylcholine (DEPC) and acyl chain perdeuterated 1,2-dipalmitoylphosphatidylcholine (DPPC-d62)/1,2-dimyristoylphosphatidylethanolamine (DMPE). The former shows gel state immiscibility over most of the composition range. The FT-IR data indicate that one of the solid phases is essentially pure DEPC, while the other solid phase contains both lipids. The DPPC-d62/DMPE pair are miscible over the entire composition range. The use of deuterated lipids as one component in the mixture permits the melting characteristics of each component to be separately determined in the FT-IR experiment. The FT-IR data are used to assign the endotherms observed in the DSC to particular molecular components. For the DPPE-d62/DEPC system, two endotherms are observed at compositions between 10 and 67 mol% DPPE-d62. The lower transition is assigned to the DEPC component, while the higher event contains contributions to the enthalpy from both lipids in the mixture. The midpoint of the DEPC melting occurs substantially below that for DPPE-d62. For the miscible pair, each of the lipids melt over approximately the same temperature range. The complementary and consistent nature of the information available from FT-IR and from DSC is demonstrated from the current work.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1986

Fourier transform infrared spectroscopic identification of gel phase domains in reconstituted phospholipid vesicles containing Ca2+-ATPase.

Ca2+-ATPase from rabbit sarcoplasmic reticulum has been isolated, purified, and reconstituted into lipid environments containing as primary components 1,2-dielaidoylphosphatidylcholine (DEPC) and acyl-chain perdeuterated 1,2-dimyristoylphosphatidylcholine (DMPC-d54). Differential scanning calorimetry (DSC) has been used to elucidate the phase behavior of this lipid pair while Fourier transform infrared spectroscopy (FT-IR) has been used to monitor the state of each lipid component in the presence of protein. The lipid mixture shows gel state miscibility over at least most of the composition range, a result in good accord with Van Dijck et al. (Biochim. Biophys. Acta 470, 58-69 (1977)), for the binary mixture with proteated DMPC. Acyl chain perdeuteration thus does not greatly alter the miscibility properties of the lipid pair. Reconstitution of Ca2+-ATPase with this lipid pair proceeds with moderate efficiency. Up to 80% of the endogenous lipid can be replaced depending on the lipid composition. Unusual composition-dependent protein-induced effects on lipid melting properties are noticed. At low levels of DMPC-d54, both the DEPC and DMPC-d54 components have their melting processes broadened and shifted to lower temperatures, compared with binary lipid mixtures of the same composition. This suggests that protein perturbs both lipids in similar fashion. At high levels of DMPC-d54, the DEPC component exhibits a highly cooperative melting process at temperatures close to that for pure DEPC. This strongly indicates that domains of DEPC are present (at least at low temperatures) in the bilayer, and that Ca2+-ATPase is excluded from these domains. The protein thus exhibits preferential interaction with the DMPC-d54 component. This work demonstrates the utility of FT-IR for identification of the molecular origin of particular domains in reasonably complex lipid mixtures. The relevance of this work to native membrane systems where lipid domains have been observed by several groups is discussed.

Calcium-Transporting ATPases↗
PubMed1986

Fourier-transform infrared studies of CaATPase/phospholipid interaction: survey of lipid classes.

CaATPase from rabbit skeletal muscle has been isolated, purified, delipidated, and reconstituted with retention of ATPase activity into lipid vesicles consisting respectively of 1,2-dipalmitoylphosphatidylethanolamine, 1-palmitoyl-2-oleoylphosphatidylethanolamine (POPE), 1-stearoyl-2-oleoylphosphatidylcholine (SOPC), and egg sphingomyelin. The effect of the enzyme on phospholipid order and melting characteristics were determined with Fourier-transform infrared spectroscopy. Taken together with prior data from this laboratory for 1,2-dipalmitoylphosphatidylcholine and 1,2-dioleoylphosphatidylcholine (DOPC), as well as for native sarcoplasmic reticulum (SR), three types of lipid response to protein incorporation have been observed: (1) Phospholipids with high levels of acyl chain unsaturation (DOPC or native SR) have their lipid acyl chains slightly ordered by CaATPase incorporation. The effect of protein on the gel-liquid crystal phase transition cannot be easily determined, since the cooperative melting even in these systems occurs at temperature well below 0 degrees C. (2) Phospholipids with saturated acyl chains show slightly lowered melting temperatures and reduced cooperativity of melting upon CaATPase insertion. In addition, protein induces (at most) slight disorder into the acyl chains at temperatures removed from the lipid melting point. (3) The strongest response is observed for phospholipids containing one saturated and one unsaturated chain (POPE or SOPC) or heterogeneous systems with low levels of unsaturation (egg sphingomyelin). In these cases, relatively low protein levels diminish the magnitude of or completely abolish the phospholipid phase transition. In addition, substantial disorder is introduced into the acyl chain compared with the pure lipid both above and below its transition temperature.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Fourier-transform infrared studies of CaATPase partitioning in phospholipid mixtures of 1,2-dipalmitoylphosphatidylcholine-d62 with 1-palmitoyl-2-oleoylphosphatidylethanolamine and 1-stearoyl-2-oleoylphosphatidylcholine.

CaATPase from rabbit sarcoplasmic reticulum has been reconstituted into binary lipid mixtures of 1-palmitoyl-2-oleoylphosphatidylethanolamine (POPE)/1,2-dipalmitoylphosphatidylcholine-d62 (DPPC-d62) and 1-stearoyl-2-oleoylphosphatidylcholine (SOPC)/DPPC-d62. Fourier-transform infrared (FT-IR) spectroscopy has been used to monitor temperature-induced structural alterations in the individual lipid components in the presence and absence of protein. A simple two-state model is used to construct a phase diagram that is in good agreement with one constructed from differential scanning calorimetry data, for the POPE/DPPC-d62 (protein-free) system. Although these two lipids are miscible over at least most of the composition range, substantial deviations from ideal behavior are observed. An estimate of the nonideality of mixing in both the gel and liquid-crystalline phases is obtained from regular solution theory. The phase diagram for SOPC/DPPC-d62 shows gel-phase immiscibility. FT-IR studies of ternary (POPE/DPPC-d62/CaATPase) complexes indicate that both lipid components are disordered by protein at all temperatures studied. In addition, their melting events are broadened and shifted to lower temperatures compared with the appropriate binary lipid mixture. Semiquantitative estimates for the fraction of each lipid melted are obtained from the model. The effect of protein on SOPC/DPPC-d62 mixtures depends on that total lipid to protein ratio. At low protein levels, SOPC is preferentially selected by CaATPase, so that bulk lipid is enriched in DPPC-d62. At high levels of protein, both lipid components are selected. The applicability of vibrational spectroscopy for determination of the partitioning preferences of membrane proteins into regions of particular chemical structure or physical order in a complex lipid environment is demonstrated.

Animals↗
PubMed1984

Aubrey James Tow.

Explore the source record for details and available documents.

Australia↗
PubMed1984

Fourier transform infrared spectroscopic studies of lipid-protein interaction in native and reconstituted sarcoplasmic reticulum.

Fourier transform infrared spectroscopy has been used to monitor lipid-protein interaction and protein secondary structure in native and reconstituted sarcoplasmic reticulum vesicles. Studies of the temperature dependence of the CH2 symmetric stretching frequency reveal no cooperative phase transitions in purified sarcoplasmic reticulum or in vesicles reconstituted with dioleoylphosphatidylcholine, although a continuous introduction of disorder into the lipid acyl chains is observed as the temperature is raised. In addition, temperature-dependent changes are observed in the Amide I and Amide II vibrations arising from protein peptide bonds. A comparison of lipid order in native sarcoplasmic reticulum and its lipid extract showed that the introduction of protein is accompanied by a slight increase in lipid order. Reconstitution of Ca2+-ATPase from sarcoplasmic reticulum with dipalmitoylphosphatidylcholine (lipid/protein ratio 30:1), reveals a perturbed lipid melting event broadened and reduced in midpoint temperature from multilamellar lipid vesicles. The onset of melting (27-28 degrees C) correlates well with the onset of ATPase activity and confirms a suggestion (Hesketh, T.R., Smith, G.A., Houslay, M.D., McGill, K.A., Birdsall, N.J.M., Metcalfe, J.C. and Warren, G.B. (1976) Biochemistry 15, 4145-4151) that a liquid crystalline environment is a requirement for optimal protein function. Finally, Ca2+-ATPase has been reconstituted into binary lipid mixtures of DOPC and acyl-chain perdeuterated DPPC. The effect of protein on the structure and melting behavior of each lipid component was monitored. The protein appears to preferentially interact with the DOPC component.

Animals↗
PubMed1984

Calorimetric and Fourier transform infrared spectroscopic studies on the interaction of glycophorin with phosphatidylserine/dipalmitoylphosphatidylcholine-d62 mixtures.

Glycophorin has been isolated in pure form from human erythrocyte membranes and reconstituted into lipid vesicles composed of binary mixtures of bovine brain phosphatidylserine (PS) and acyl-chain perdeuterated dipalmitoylphosphatidylcholine (DPPC-d62). The effect of protein on lipid melting behavior and order has been monitored with differential scanning calorimetry and Fourier transform infrared spectroscopy (FT-IR). The phase diagram for PS/DPPC-d62 is consistent with that previously reported for PS/DPPC (Stewart et al. (1979) Biochim. Biophys. Acta 556, 1-16) and indicates that acyl chain perdeuteration does not greatly alter the lipid mixing characteristics. The use of deuterated lipid allows the examination of lipid order by FT-IR of each lipid component in the binary mixtures as well as in the ternary (lipid/lipid/protein) systems. Addition of glycophorin to a 30:70 PS/DPPC-d62 binary lipid mixture results in a preferential glycophorin/PS interaction leading to bulk lipid enriched in DPPC-d62. This is revealed in two ways: first, through cooperative calorimetric transitions increased in temperature from the binary lipid system and second, through FT-IR melting curves of the DPPC-d62 component which shows transitions increased in both onset and completion temperatures in the presence of protein. In addition, non-cooperative melting events are observed at temperatures below the onset of phase separation. The FT-IR data are used to assign these non-cooperative events to the melting of the PS component. For the 50:50 lipid mixture with protein, two transitions are observed in the DSC experiments. The IR results indicate that both lipid components are involved with the lower temperature event.

Animals↗
PubMed1984

Interaction of glycophorin with phosphatidylserine: a Fourier transform infrared investigation.

Glycophorin, from the human erythrocyte membrane, has been isolated in pure form and reconstituted into unilamellar vesicles with bovine brain phosphatidylserine (PS). Fourier transform infrared spectroscopy has been used to monitor the protein conformation as well as the effect of protein on lipid order and melting. Glycophorin, at levels of 1 mol %, nearly abolishes the gel to liquid-crystal phase transition seen in pure PS vesicles between 8 and 16 degrees C by inducing significant disorder into the lipid gel phase. A transition of reduced magnitude remains between 14 and 22 degrees C in the lipid/protein complexes. Evidence is presented for specific interaction of glycophorin with the interfacial region of PS. In general, the effects on lipid melting produced by protein at the 1 mol % level are more pronounced than those noted in a previous study of glycophorin/phosphatidylcholine interactions [ Mendelsohn , R., Dluhy , R. A., Taraschi , T., Cameron, D., & Mantsch , H.H. (1981) Biochemistry 20, 6699-6706]. Two bands are observed for the protein amide I (C = O stretching) mode. A main feature at 1653 cm-1 indicates that the bulk of the secondary structure is random coil or alpha-helical. A weaker shoulder at 1675 cm-1 suggests the occurrence of a small proportion of the beta-sheet form. The results confirm circular dichroism studies of Schulte & Marchesi (1979) [ Schulte , T.H., & Marchesi , V.T. (1979) Biochemistry 18, 275-280]. Fourier transform infrared (FT-IR) studies of a ternary complex of PS/dipalmitoyl-phosphatidylcholine- d62 (DPPC- d62 )/glycophorin indicate that the glycophorin preferentially interacts with the PS component.(ABSTRACT TRUNCATED AT 250 WORDS)

Erythrocyte Membrane↗
PubMed1983

Interaction of dipalmitoylphosphatidylcholine and dimyristoylphosphatidylcholine-d54 mixtures with glycophorin. A fourier transform infrared investigation.

Glycophorin from the human erythrocyte membrane has been isolated in pure form and reconstituted into large unilamellar vesicles comprised of binary mixtures of 1,2-dipalmitoyl-3-sn-phosphatidylcholine (DPPC) and chain perdeuterated 1,2-dimyristoyl-3-sn-phosphatidylcholine (DMPC-d54). The effect of temperature and protein on lipid structure and mixing was monitored by using Fourier transform infrared spectroscopy; deuteration of one of the components of the mixture permits observation of the protein interaction with each lipid species. The melting curves were analyzed by assuming that each lipid chain can exist in one of two physical states (i.e., gel or liquid crystalline), characterized by a temperature-dependent Lorentzian distribution for the line shape of the C-H or C-D stretching vibrations. The fraction of each lipid component melted at temperatures within the two-phase region of the phase diagram was calculated and approximate phase diagrams were constructed. Addition of protein lowers the liquidus line of the phase diagram while leaving the solidus line essentially unchanged. No lipid phase separation is observed. The effect of protein is more pronounced on the DPPC component than on the DMPC-d54. The former is significantly more disordered and/or fluidized at all lipid mole fractions in the ternary system than in the binary phospholipid mixture.

Dimyristoylphosphatidylcholine↗
PubMed1982

Do clinical levels of general anaesthetics affect lipid bilayers? Evidence from Raman scattering.

We have used Raman spectroscopy to investigate the effects of the general anaesthetics halothane and chloroform on lipid bilayer order. Clinical concentrations of these anaesthetics had no significant effect on the hydrocarbon chain conformation in multilamellar vesicles of dimyristoylphosphatidylcholine/cholesterol. This result was obtained with a technique sufficiently precise to monitor changes in the acyl chain trans-gauche population ratio associated with a 1-2 K alteration in temperature. Very high levels of anaesthetics caused a marked disordering of the hydrocarbon chains. The danger of inferring an effect at clinical concentrations from data obtained at much higher levels is illustrated by a statistical analysis of our dose-response curves.

Cholesterol↗
PubMed1982

Order and fluidity in the terminal methyl region of dipalmitoyl phosphatidylcholine multibilayers: a comparison of Raman and 2H-NMR spectroscopy.

Deuterium magnetic resonance (2H-NMR) and Raman spectroscopy are used to investigate order and fluidity at the terminal methyl position in 16-d3, 16'-d3 dipalmitoylphosphatidyl-choline (16-d6 DPPC) multibilayers. These methods reveal substantial motion and disorder in the gel phase, 5-10 degree C below the gel-liquid crystal phase transition temperature (Tm). The phase transition is sensed in the 2H-NMR spectrum as a reduction in the quadrupole splitting from 14 kHz to approximately 3 kHz. In contrast, the Raman parameter used to characterize the CD3 vibrations is quite insensitive to the melting process, although an analagous parameter does sense disordering at Tm at the 10 and 10' position in 10-d2, 10'-d2 DPPC. The difference in the response of the NMR and Raman parameters may arise because the vibrational spectrum of the CD3 group is inhomogeneously broadened and is therefore quite sensitive to alterations in the local environment around the methyl group. In contrast, the NMR quadrupole splitting is sensitive to both local motion of the methyl group and, near Tm, to motions of the CD2 group induced by transgauche isomerizations further up the chain. The difficulties that arise when results from different spectroscopic techniques are compared are demonstrated.

Lipid Bilayers↗