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Biomedical subjects

K Gawrisch

Publications and source records attributed to K Gawrisch.

47 records · Page 3Linked to original sources
PubMed1986

Hydration properties and structure of phosphatidylcholine membranes in the presence of n-nonyl bromide.

Interaction of chemical fusogen n-nonyl bromide with a model membrane formed from phosphatidylcholine was studied using 2D-NMR spectra of heavy water and 31P-NMR proton decoupled spectra of the lipid phosphate group in multilamellar lipid dispersions. n-Nonyl bromide was found to influence the hydration layer of the model membrane. No participation of phosphatidylcholine molecules in non-bilayer configurations of the membrane was observed.

Deuterium↗
PubMed1985

The dielectric properties of aqueous solutions of poly(ethylene glycol) and their influence on membrane structure.

The dielectric constant of water is reduced drastically on addition of poly(ethylene glycol). The behaviour is not described by a linear mixture equation. The decreased dielectric constant can lead to the general perturbation of the membrane structure which is necessary in such a manner that a strong aggregation of membranes would lead to their fusion. The changed cation permeability in the presence of poly(ethylene glycol) can explained as the effect of the lowered dielectric constant on the transfer energy.

Electric Conductivity↗
PubMed1985

[Synthesis and biologic activity of some stable structure analogs of platelet activating factor].

Physiologically stable structure analogues of the platelet-activating factor (PAF-acether), the acetyl group of which had been substituted by short-chain alkyl rests, had been synthesized and been tested with regard to their biological activity against thrombocytes. Five differently substituted 2-alkylmalonic acid esters with methyl rest up to n-pentyl rest had been applied the basic products. The n-propyl compound exhibits the most intense biological activity, which is, however, essentially reduced against the PAF-acether. With conditions of the examination, all the other derivatives possess a more decreased activity.

Chemical Phenomena↗
PubMed1983

Effect of poly(ethylene glycol) on phospholipid hydration and polarity of the external phase.

The hydration properties of phosphatidylcholine (PC)/water dispersions on the addition of poly(ethylene glycol) were studied by means of 2H-NMR. The quadrupole splittings and their temperature dependences correspond to measurements of PC/water dispersions at low water content. It is concluded that the bound water is partly extracted by poly(ethylene glycol) but the binding properties of the water in the inner hydration shell of about five water molecules are not changed. The ability of some phospholipid/water dispersions to undergo phase transitions to nonlamellar structures upon dehydration is discussed. Dipalmitoylphosphatidylcholine (DPPC) and egg phosphatidylcholine do not form nonlamellar structures on addition of purified poly(ethylene glycol), as was demonstrated by means of 31P-NMR. Poly(ethylene glycol) decreases the polarity of the aqueous phase and the partition of hydrophobic molecules between the membrane and the external phase is changed. This was demonstrated using the excimer fluorescence of pyrene in a ghost suspension. It is suggested that the changes in polarity and hydration on the addition of poly(ethylene glycol) can contribute to the alterations in the membrane surface observed under conditions of membrane contact and fusion.

Cell Fusion↗
PubMed1983

Effect of the local anesthetic heptacaine hydrochloride on the structured water in model phosphatidylcholine membrane: 2D-NMR and 31P-NMR study.

Interaction of the local anesthetic 1[2-(2-heptyloxyphenyl-carbamoyloxy)-ethyl] piperidinium chloride (heptacaine hydrochloride) with a model membrane formed by phosphatidylcholine was studied using 2D-NMR spectra of heavy water and 31P-NMR proton-decoupled and undecoupled spectra of the lipid phosphate group. Heptacaine hydrochloride was found to increase the number of water molecules oriented over the polar region of the membrane, to increase the order parameter of the lipid phosphate group, as well as that of oriented water, and to increase the volume of unoriented water trapped between the bilayers. Heptacaine hydrochloride also affects the temperature dependence of quadrupolar splitting of oriented heavy water deuterons. Heptacaine hydrochloride is suggested to expand the membrane laterally and to charge the membrane surface electrostatically.

Chemical Phenomena↗
PubMed1982

Optical detection of phase transitions in simple and mixed lipid-water phases.

A simple method for the detection of phase transitions in lipid-water systems by recording the intensity of the transmitted light through a sample placed between crossed polarizers as a function of the temperature was developed. A very small amount of lipid material is sufficient for its effective application. Two zwitterionic lipids in water, dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylethanolamine (DPPE) as well as their mixtures were studied by means of this method. The results were compared with differential scanning calorimetry (DSC) data and a good correspondence was established. A phase diagram of the DPPC-DPPE mixture is constructed. This study also throws additional light on the nature of the 'pretransition' of DPPC.

Birefringence↗
PubMed1981

31p-NMR investigations of phase separation in phosphatidylcholine/phosphatidylethanolamine mixtures.

A phase diagram of DPPC-DPPE mixture is constructed by an analysis of the temperature dependence of the anisotropy of chemical shift of the 31P-NMR signals of the individual components. At each temperature the phase state of the individual phospholipids is described. Thus 31P-NMR is more informative than other methods such as ESR, DSC and fluorescence. The measurements confirm the conclusion of other authors that there is a phase separation in the gel state. In the temperature range of the phase transition the molecules are exchanged rapidly between liquid-crystalline and solid regions. In addition to the phase diagram a theoretical approach is applied to estimate the relative distribution of like and unlike molecules in the liquid-crystalline state and a nonrandom distribution is found.

Magnetic Resonance Spectroscopy↗
PubMed1977

NMR and calorimetric studies of changes in phase transition of head group modified phospholipids.

The 13C- and 31P-NMR spectra and DSC thermograms of unsonicated dispersions consisting of phospholipids of varying methylation stages of the propanolamine head group were investigated. Methylation of the head group was accompanied by a corresponding reduction in the phase transition temperatures. In the liquid crystalline state the 31P-anisotropy of the chemical shift is about equal for all studied compounds, demonstrating that the motion of the phosphate group is not influenced by modifications of the propanolamine group.

Calorimetry↗
PubMedDate not supplied

Effect of the conformation of a peptide from gp41 on binding and domain formation in model membranes.

Binding of the peptide fragment 828-848 (P828), amino acid sequence RVIEVVQGACRAIRHIPRRIR, from the carboxy-terminal region of the envelope glycoprotein gp41 of human immunodeficiency virus type 1 (HIV-1) to membranes composed of a mixture of neutral and negatively charged phospholipids results in domain or cluster formation of the charged lipid. The conformation and dynamics of the peptide are investigated in solution and in the presence of sodium dodecyl sulphate (SDS) micelles using high resolution nuclear magnetic resonance (NMR) spectroscopy and circular dichroism (CD) spectropolarimetry. The CD results demonstrate that addition of either SDS, negatively charged phospholipid liposomes, or trifluoroethanol (TFE) induces a conformational transition of the peptide from a random coil or an extended chain in water to a more ordered structure with an estimated helical content of up to 60%. The structure of the peptide in a membrane mimetic SDS solution was investigated in detail using two-dimensional NMR. The measurements demonstrate the existence of a helical component in the peptide conformation in the SDS-bound state. The peptide most likely exists as an ensemble of conformations with exchange times between them which are fast on the chemical shift NMR time scale (10(-3) s). Simple neutralization of the six arginine sidechain charges does not cause the peptide to adopt an ordered structure. Thus, there is an additional requirement for the structural transition such as that resulting from constraint of the peptide on a surface, or localization of the peptide at the lipid-water interface where the polarity is lower.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMedDate not supplied

Role of interactions at the lipid-water interface for domain formation.

The lipid-water interface is critical for the packing of lipid molecules in membranes. We have demonstrated that lateral phase separation in membranes can be driven by electrostatic interactions such as those involving charged lipid species and oppositely charged peptides, in addition to hydration effects at the lipid-water interface. By using nuclear magnetic resonance (NMR), circular dichroism and fluorescence spectroscopy we have shown that binding of a 21-amino acid peptide containing six positively charged arginine residues to mixed phosphatidylcholine (PC)/phosphatidylglycerol (PG) membranes results in a conformational change in the peptide from a random coil to a helical structure and causes the formation of domains of negatively charged PG. Binding of the peptide to PG membranes disorders the lipid hydrocarbon chains. The strength of lipid-peptide binding at the interface, the conformational change in the peptide, and domain formation with the negatively charged lipid are coupled energetically. The lipid-peptide association constant is lower for membranes containing 20 mol% PG in PC/PG mixtures than for 100% PG membranes. We suggest that one of the factors that lower the association constant in PC/PG membranes is entropic energy of formation of PG domains. Besides electrostatic interactions, hydration of lipids is important for domain formation. We have shown that dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylethanolamine separate under conditions of decreased water activity. Furthermore, water activity controls lipid packing stress in the hydrocarbon core and the headgroups of membranes as demonstrated by induction of an inverse-hexagonal-to-lamellar phase transition in dioleoylphosphatidylethanolamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗