The structure of membranes and membrane proteins embedded in amorphous ice

1992 ◽  
Vol 50 (1) ◽  
pp. 432-433
Author(s):  
Uwe Lücken ◽  
Joachim Jäger
Keyword(s):  
Phase Transition ◽  
Transition Temperature ◽  
Membrane Proteins ◽  
Phase Transition Temperature ◽  
Lipid Vesicles ◽  
Freezing Stress ◽  
Amorphous Ice ◽  
Different Temperatures ◽  
Band Pass ◽  
Lipid Polymorphism

TEM imaging of frozen-hydrated lipid vesicles has been done by several groups Thermotrophic and lyotrophic polymorphism has been reported. By using image processing, computer simulation and tilt experiments, we tried to learn about the influence of freezing-stress and defocus artifacts on the lipid polymorphism and fine structure of the bilayer profile. We show integrated membrane proteins do modulate the bilayer structure and the morphology of the vesicles.Phase transitions of DMPC vesicles were visualized after freezing under equilibrium conditions at different temperatures in a controlled-environment vitrification system. Below the main phase transition temperature of 24°C (Fig. 1), vesicles show a facetted appearance due to the quasicrystalline areas. A gradual increase in temperature leads to melting processes with different morphology in the bilayer profile. Far above the phase transition temperature the bilayer profile is still present. In the band-pass-filtered images (Fig. 2) no significant change in the width of the bilayer profile is visible.

scholarly journals Mechanical, Electrical, and Biological Properties of Mechanochemically Processed Hydroxyapatite Ceramics

Nanomaterials ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 2216
Author(s):  
Sujata Swain ◽  
Rakesh Bhaskar ◽  
Mukesh Kumar Gupta ◽  
Sonia Sharma ◽  
Sudip Dasgupta ◽  
...  
Keyword(s):  
Phase Transition ◽  
Cell Proliferation ◽  
Transition Temperature ◽  
Phase Transition Temperature ◽  
Sintering Temperature ◽  
Biological Properties ◽  
Hydroxyapatite Ceramics ◽  
Different Temperatures ◽  
Orientational Motion ◽  
Type Of Behavior

The effect of the sintering temperature on densification and the resultant mechanical, electrical, and biological properties of mechanochemically processed hydroxyapatite (HAp) samples was investigated. HAp samples were sintered at 1200, 1250, and 1300 °C for 4 h, respectively. HAp samples sintered at 1250 °C showed better mechanical properties, which was attributed to their smaller grain size compared to HAp samples at higher sintering temperatures. The nearly identical value of the dielectric constant (εr) and better cell proliferation was exhibited by HAp samples sintered at 1250 and 1300 °C, respectively. At ~210 °C, in all the samples sintered at different temperatures, a dielectric anomaly was obtained, which was attributed to the phase transition temperature of the HAp system. Dielectric properties near the phase transition temperature showed a dielectric relaxation-type of behavior, which was attributed to the re-orientational motion of OH− ions in the HAp system. Higher cell proliferation and viability were exhibited by the HAp1300 samples, whereas comparatively equivalent cell growth and higher mechanical strength were observed in the HAp1250 samples.

The effect of cholesterol on the interaction of glucagon with the gel state of dimyristoylphosphatidylcholine

1980 ◽  
Vol 58 (10) ◽  
pp. 859-864 ◽  
Author(s):  
Richard M. Epand
Keyword(s):  
Phase Transition ◽  
Transition Temperature ◽  
Light Scattering ◽  
Membrane Proteins ◽  
Phase Transition Temperature ◽  
Lipid Binding ◽  
Starting Material ◽  
Scatchard Analysis ◽  
Lipid Interactions ◽  
Fluorescence Measurements

Cholesterol has a large effect on the binding of glucagon to dimyristoylphosphatidylcholine (DMPC) and to dipalmitoylphosphatidylcholine (DPPC). At cholesterol concentrations of 20 mol% or greater there is virtually no interaction of glucagon with phospholipid. Glucagon can, however, solubilize DMPC or DPPC with 10% cholesterol. In the case of DPPC the solubilized lipid is depleted of cholesterol relative to the starting material. These results suggest that glucagon excludes cholesterol from its surroundings.It is shown from solubility, light scattering, and glucagon fluorescence measurements that the glucagon–DMPC complex containing 10% cholesterol is stable only in the region of the phase transition temperature. Scatchard analysis of lipid binding to glucagon indicates a decrease in the amount of bound lipid below 22 °C or above 24 °C. The effect of the phase transition on the interaction of glucagon with lipids is compared with that found for other membrane proteins. Several aspects of the effect of cholesterol on glucagon–lipid interactions are analogous to effects which have been observed with serum apolipoproteins.

scholarly journals Study of the interaction between the antitumour protein α-sarcin and phospholipid vesicles

1989 ◽  
Vol 258 (2) ◽  
pp. 569-575 ◽  
Author(s):  
M Gasset ◽  
A Martinez del Pozo ◽  
M Oñaderra ◽  
J G Gavilanes
Keyword(s):  
Phase Transition ◽  
Transition Temperature ◽  
Ionic Strength ◽  
Phase Transition Temperature ◽  
Acyl Chain ◽  
Lipid Vesicles ◽  
Model Systems ◽  
Molar Ratio ◽  
Phospholipid Vesicles ◽  
Acidic Vesicles

alpha-Sarcin is a single polypeptide chain protein which exhibits antitumour activity by degrading the larger ribosomal RNA of tumour cells. We describe the interaction of a alpha-sarcin with lipid model systems. The protein specifically interacts with negatively-charged phospholipid vesicles, resulting in protein-lipid complexes which can be isolated by ultracentrifugation in a sucrose gradient. alpha-Sarcin causes aggregation of such vesicles. The extent of this interaction progressively decreases when the molar ratio of phosphatidylcholine increases in acidic vesicles. The kinetics of the vesicle aggregation induced by the protein have been measured. This process is dependent on the ratio of alpha-sarcin present in the protein-lipid system. A saturation plot is observed from phospholipid vesicles-protein titrations. The saturating protein/lipid molar ratio is 1:50. The effect produced by the antitumour protein on the lipid vesicles is dependent on neither the length nor the degree of unsaturation of the phospholipid acyl chain. However, the aggregation is dependent on temperature, being many times higher above the phase transition temperature of the corresponding phospholipid than below it. The effects of pH and ionic strength have also been considered. An increase in the ionic strength does not abolish the protein-lipid interaction. The effect of pH may be related to conformational changes of the protein. Binding experiments reveal a strong interaction between alpha-sarcin and acidic vesicles, with Kd = 0.06 microM. The peptide bonds of the protein are protected against trypsin hydrolysis upon binding to acidic vesicles. The interaction of the protein with phosphatidylglycerol vesicles does not modify the phase transition temperature of the lipid, although it decreases the amplitude of the change of fluorescence anisotropy associated to the co-operative melting of 1,6-diphenyl-1,3,5-hexatriene (DPH)-labelled vesicles. The results are interpreted in terms of the existence of both electrostatic and hydrophobic components for the interaction between phospholipid vesicles and the antitumour protein.

Evidence for the regulation of the activity of protein kinase C through changes in membrane properties

1991 ◽  
Vol 11 (1) ◽  
pp. 59-64 ◽  
Author(s):  
Richard M. Epand ◽  
Raquel F. Epand ◽  
Bryan T.-C. Leon ◽  
Fredric M. Menger ◽  
J. F. Kuo
Keyword(s):  
Phase Transition ◽  
Protein Kinase C ◽  
Transition Temperature ◽  
Protein Kinase ◽  
Phase Transition Temperature ◽  
Hexagonal Phase ◽  
Lipid Phase ◽  
Kinase C ◽  
Protein Kinase C Activity ◽  
Lipid Polymorphism

We measured the effects of two branched-chain analogs of distearoyl-phosphatidylcholine, containing either a methyl or an n-butyl group at the 8 position, on the bilayer to hexagonal phase transition temperature of dielaidoylphosphatidylethanolamine. The former compound raised the bilayer to hexagonal phase transition temperature while the latter compound lowered it. The opposite effects of these amphiphiles on protein kinase C activity (inhibition and activation, respectively) correlated with their effects on lipid polymorphism. Because of the similarity of the structures of these two compounds, it seems likely that their opposite effects on the activity of protein kinase C is a result of their alteration of the lipid environment of the membrane rather than to binding to a specific site on the protein. We also compared the effects of hexachlorophene on lipid polymorphism and protein kinase C activity at high and at low calcium concentrations. We also found that the effect of hexachlorophene forming a complex with Ca2+ is to increase both the hexagonal phase forming propensity of the membrane as well as to increase the activity of protein kinase C, again demonstrating the correlation between lipid phase propensity and effects on protein kinase C activity.

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