ISSN:0005-9021    

DOI:10.1002/bbpc.198800238

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1988

数据来源: WILEY

摘要:

AbstractProperties of the biological and model membranes can be regulated by the lipid polar headgroups and their bathing solution. This occurs primarily via changes in the interfacial hydrophilicity and hydration, which are mostly a result of the lipid deprotonation or osmotic dehydration. Steric or electrostatic effects normaly play a minor role. Therefore, phosphate derivatization or protonation, further changes that decrease the lipid capacity for the hydrogen bonding and lower the interfacial affinity for binding water, as well as any system alterations that diminish the amount of interbilayer water can all cause the lipid chain melting phase transition temperature, the persistence of the lamellar lipid phase, and the colloidal stability of vesicle suspension, but also the height of the membrane permeability barrier to decrease, whereas lipid protonation or dealkylation have the reverse effect. – Lipid bilayers and their adjacent solution behave as single thermodynamic entity. Changes in the polar headgroup region and in the solvent composition consequently can regulate not only the membrane capacity for molecular or supramolecular reorganisation (e.g. phase changes or membrane fusion, respectively) but moreover may govern the short‐range intermembrane (e.g. hydration) forces and, to some extent, affect the membrane‐solute interactions. These effects are therefore of considerable interest and relevance for the studies and understanding of membrane binding and tran

ISSN:0005-9021    

DOI:10.1002/bbpc.198800240

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1988

数据来源: WILEY

摘要:

AbstractTransient defect structures in thermodynamic equilibrium with the membrane lattice are considered to be major pathways for the passive permeation of small and neutral (with the possible exception of protons) molecules. Results on the water permeation and on the transfer of protons across erythrocyte membranes are discussed. The inhibition/stimulation of transport rates is interpreted in terms of specific or global actions of the inhibitory/stimulatory molecules on lipid/protein and protein/protein assemblies.

ISSN:0005-9021    

DOI:10.1002/bbpc.198800241

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1988

数据来源: WILEY

摘要:

AbstractFT‐IR and2H‐NMR‐spectroscopy has been used to study structure and dynamics of specifically labeled phospholipids in model membranes. Three examples for the application of these two spectroscopic techniques are given. 1.2H‐NMR‐spectroscopy can be used to study the behavior of pure specifically deuterated model compounds of phospholipids with different head groups like phosphatidylcholines (PC**)) and phosphatidylethanolamines (PE). Line shape simulations of powder spectra and of spectra of oriented samples provide information on the mechanism and correlation times of the molecular reorientations. In mixtures of phospholipids with different head groups2H‐NMR‐spectroscopy can be used to study the mixing behavior of lipids. Evidence for lipid clustering in the liquid‐crystalline phase comes from different splittings observed for the two components. 2. FT‐IR‐spectroscopy of13C = O labeled phospholipids gives information on the hydration behavior of the glycerol back bone. Because of the vibrational isotope effect both carbonyl bands of the ester groups of the lipid can be observed separately when one of the C = O groups is labeled with13C. FT‐IR spectra indicate that both ester carbonyl groups of lipids in hydrated membranes are in contact with water. The amount of hydration depends on the phase state and the nature of the lipid head groups. 3. A combination of2H‐NMR and FT‐IR‐spectroscopy was used to determine structure and dynamics of phospholipids with ω‐cyclohexyl fatty acids. Drastic differences in conformational and dynamical behavior between odd‐ and even‐numbered members of

ISSN:0005-9021    

DOI:10.1002/bbpc.198800242

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1988

数据来源: WILEY

摘要:

AbstractNew fluorescent glucagon derivatives were synthesized by converting tryptophan25to 2‐thiol‐tryptophan with the consequent use of thiol specific fluorescent reagents. All derivatives retained the ability to bind tightly to rat liver membranes and rat hepatocytes in primary culture and to activate adenylate cyclase as potently as native glucagon. Thus these derivatives are full agonists. From experiments with monolayer cultured hepatocytes and125I‐glucagon at elevated temperatures it was assumed that the ligand was internalised at this temperature since some of the specifically bound ligand could no longer be washed off with acid. This was confirmed in experiments where monolayer cultures of hepatocytes were incubated with the fluorescein‐labelled derivates of glucagon, thus allowing the study of the distribution of glucagon specifically bound on the cell surface using video intensification microscopic techniques. In keeping with autoradiographic studies using radiolabelled glucagon, or electron microscope studies using ferritin labelled glucagon, we could now show using fluorescently labelled glucagon derivatives and video intensification microscopy that at lower temperatures the bound ligand was distributed all over the cell surface. Whereas, at the higher temperature, ligand derived fluorescence could only be detected in mobile intracellular vesicles following internalisation and removal from the cell

ISSN:0005-9021    

DOI:10.1002/bbpc.198800243

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1988

数据来源: WILEY

摘要:

AbstractThe intramolecular reactions of membrane proteins are investigated by the new developed time resolved FTIR difference spectroscopy technique. By this technique the kinetics of single groups in membrane proteins can be determined. As example the protonation kinetics of aspartic acids are shown. Simultaneously the absorbance change in the visible spectral region is measured at one wavelength. Thereby the IR‐Absorbance changes can be correlated to changes in the visible spectral region. The technique is applied to the lightdriven proton pump bacteriorhodopsin and to crystals of the photosynthetic reaction center of Rps. viridi

ISSN:0005-9021    

DOI:10.1002/bbpc.198800244

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1988

数据来源: WILEY

摘要:

AbstractElectron spin resonance techniques were employed to investigate the interaction of sialic acid bearing carbohydrates covalently bound to gangliosides or glycophorin with membrane surfaces. In phosphatidylcholine membranes it was found that gangliosides induce a rigidification. This hydrophobic effect is partially compensated by a hydrophilic interaction with the membrane surface. In phosphatidylethanolamine membranes ganglioside GD1ais the only one that reduces the lipid phase transition temperature. We assume a special oligosaccharide conformation, that strongly disturbs the hydrogen bond network of the PE host membrane. The results are further supported by experiments with reconstituted glycophorin containing membranes. In a phosphatidylcholine matrix we observed the formation of an immobilized lipid domain that surrounds the protein. Phosphatidylethanolamines within a phosphatidylcholine membrane are excluded from such a domain. This is also interpreted by the formation of hydrogen bonds between sialic acid groups of the protein and the amino functions of the lipid headgroups.

ISSN:0005-9021    

DOI:10.1002/bbpc.198800245

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1988

数据来源: WILEY

摘要:

AbstractCharge‐pulse experiments were performed on membranes made of dioleoyl phosphatidylcholine/n‐decane in the presence of 4 structural analogs of tetraphenylborate (TPB, triphenylcyanoborate (TPCB), tetrakis (4‐fluorophenyl)borate (TFPB), tetrakis (4‐chlorophenyl)borate (TCPB), and tetrakis (3‐trifluoromethylphenyl)borate (TTFPB)). The analysis of the experimental results using a previously proposed model allowed the calculation of the partition coefficient, β, and of the translocation rate constant,ki, of the lipophilic ions. The adsorption of the different TPB‐analogs to the membranes was similar, whereas their structure had a dramatic influence on the translocation rate constants and they increased by almost six orders of magnitude from TPCB to TTFPB. The free energy of the ions in the membranes as calculated from the translocation rate constants, decreased from TPCB to TTFPB by about 31 kJ/mol (7.4 kcal/mol). The change of the free energy in the membrane was used for the estimation of an effective radius of the TPB‐analogs with respect to the van der Waals

ISSN:0005-9021    

DOI:10.1002/bbpc.198800246

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1988

数据来源: WILEY

ISSN:0005-9021    

DOI:10.1002/bbpc.198800247

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1988

数据来源: WILEY

摘要:

AbstractJunctional coupling was studied in murine pancreatic acinar cells using the double whole cell patch clamp method. Independent of the electrolyte composition of the pipette solution, cell pairs spontaneously uncoupled. Addition of 5 mM ATP and 0.1 mM cAMP to the pipette electrolyte was sufficient to stabilize electrical coupling within an observation time of over one hour. At stable cell‐to‐cell‐coupling superfusion of a cell pair by 1‐oleyl‐2‐acetylglycerol (OAG) containing bath solutions induced a progressive decrease of coupling after a delay of about 10 minutes. Under these conditions stepwise changes of the junctional conductance of about 45 pS and 90 pS could be identified. Similarity, addition of protein kinase C to the pipette solution reduced junctional coupling. An antagonistic effect of protein kinase A and protein kinase C dependent processes on the permeability of gap junctions i

ISSN:0005-9021    

DOI:10.1002/bbpc.198800248

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1988

数据来源: WILEY