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M Gaestel

Publications and source records attributed to M Gaestel.

77 records · Page 5Linked to original sources
PubMed1984

A theoretical approach to cluster formation in biological membranes.

A theoretical analysis of cluster formation within the lipid matrix of biological membranes is presented. Various models are analysed: (a) one-dimensional monolayer, (b) two-dimensional monolayer and (c) one dimensional bilayer. Furthermore, lipid-protein interactions are considered. The model is based on differential equations for the probabilities ai and bi which characterize the occupation of the lattice site i by the lipids A and B, respectively. These differential equations are an approximation of the Master-equation. Steady states as well as time-dependent variations are analysed. Depending on the interaction energies of the two lipids, different stationary lipid distributions are obtained, including clusters of lipids A or B and alternating structures. The distributions may be dynamically stable or unstable. It is shown that phase transitions within the lipid matrix may be induced by alteration of the composition of the membrane, by changing the interaction energies of the lipids, by variation of the temperature or by lipid-protein interactions. The transitions between different stationary distributions are studied by use of bifurcation diagrams. The analysis of time-dependent states reveals that unstable structures of the membrane may be important for certain time periods. Consideration of the lipid bilayer leads to a great number of possible distributions, which may be symmetric or asymmetric with respect to the outer and inner leaflets of the membrane.

Membrane Lipids↗
PubMed1983

Lateral lipid distribution and phase transition in phosphatidylethanolamine/phosphatidylserine vesicles. A cross-linking study.

To determine the nonideal mixing of two lipid components within the membrane, lipid cross-linking experiments were carried out on dipalmitoylphosphatidylethanolamine (DPPE) vesicles and on dipalmitoylphosphatidylethanolamine/dipalmitoylphosphatidylserine (DPPE/DPPS) vesicles. By comparison of the cross-linking reactions on both types of vesicle the mean neighbourhood relations within the binary lipid mixture can be obtained. To elucidate the relationship between cluster formation and phase transition, the temperature dependences of the lipid arrangement within the vesicle membrane and of the lipid order parameter describing the fluidity of the membrane were measured. Cluster size and phase transition correlate: during the phase transition of the lipid species with the lower phase-transition temperature (DPPS) the nonideality of the mixture increases by phase separation. Above the phase transition temperature of the second lipid species (DPPE) the clusters disappear and a slight alternating lipid arrangement is characteristic of the fluid phase.

Chemical Phenomena↗
PubMed1981

The electric potential across the erythrocyte membrane: a mathematical model.

The space-dependent electric potential of erythrocyte membranes is determined on the basis of a mathematical model which takes into account the membrane surface charges of glycophorine A, spectrin and phosphatidyl serine. The calculations are performed by numerical integration of the nonlinear Poisson-Boltzmann-equation.

Erythrocyte Membrane↗
PubMedDate not supplied

The effect of the intersubunit disulfide bond on the structural and functional properties of the small heat shock protein Hsp25.

The murine small heat shock protein Hsp25 carries a single cysteine residue in position 141 of its amino acid sequence. Interestingly, Hsp25 can exist within the cell as covalently bound dimer which is linked by an intermolecular disulfide bond between two monomers. Oxidative stress caused by treatment of the cells with diamide, arsenite, or hydrogen peroxide leads to an increase in Hsp25-dimerisation which can be blocked by simultaneous treatment with reducing agents. Recombinant Hsp25 was prepared in an oxidized dimeric (oxHsp25) and reduced monomeric (redHsp25) from. The two species were compared with regard to secondary structure, stability, oligomerization properties and their chaperone activity. It is demonstrated by CD measurements in the far UV region that there are no significant differences in the secondary structure and temperature- or pH-stability of oxHsp25 and redHsp25. However, according to CD measurements in the near UV region an increase in the asymmetry of the microenvironment of aromatic residues in oxHsp25 is observed. Furthermore, an increase in stability of the hydrophobic environment of the tryptophan residues mainly located in the N-terminal domain of the protein against urea denaturation is detected in oxHsp25. Both reduced and oxidized Hsp25 from oligomeric complexes of similar size and stability against detergents and both species prevent thermal aggregation of citrate synthase and assist significantly in oxaloacetic acid-induced refolding of the enzyme. Hence, the overall secondary structure, the degree of oligomerization and the chaperone activity of Hsp25 seem independent of the formation of the intermolecular disulfide bond and only the stability of the hydrophobic N-terminal part of the molecule is influenced by formation of this bound. The obtained data do not exclude the possible involvement of dimerization of this protein in other cellular functions, e.g. in intracellular sulfhydryl-buffering or in the protection of actin filaments from fragmentation upon oxidative stress.

Amino Acid Sequence↗