scholarly journals Biological membranes as bilayer couples. III. Compensatory shape changes induced in membranes.

1976 ◽  
Vol 70 (1) ◽  
pp. 193-203 ◽  
Author(s):  
M P Sheetz ◽  
R G Painter ◽  
S J Singer
Keyword(s):  
Biological Membranes ◽  
Bilayer Membrane ◽  
Membrane Curvature ◽  
The Other ◽  
Rational Basis ◽  
Asymmetric Membranes ◽  
Shape Changes ◽  
Bilayer Couple

We have previously proposed the hypothesis that asymmetric membranes behave like bilayer couples: the two layers of the bilayer membrane can respond differently to a particular perturbation. Such a perturbation, for example, can result in the expansion of one layer relative to the other, thereby producing a curvature of that membrane. In experiments with erythrocytes and lymphocytes, we now demonstrate that different membrane perturbations which have opposite effects on membrane curvature can compensate and neutralize one another, as expected from the bilayer couple hypothesis. This provides a rational basis, for example, for understanding the effects of amphipathic drugs on a variety of cellular phenomena which involve shape changes of membranes.

scholarly journals Equilibrium and kinetic effects of drugs on the shapes of human erythrocytes.

1976 ◽  
Vol 70 (1) ◽  
pp. 247-251 ◽  
Author(s):  
M P Sheetz ◽  
S J Singer
Keyword(s):  
Cell Shape ◽  
Human Erythrocytes ◽  
The Other ◽  
Equilibrium Conditions ◽  
Membrane Perturbation ◽  
Preferential Binding ◽  
Kinetic Effects ◽  
Shape Changes ◽  
Bilayer Couple ◽  
Outer Half

We have previously proposed that if the two half-layers of a membrane are different in their protein and lipid compositions, they may respond differently to some membrane perturbation (the bilayer couple hypothesis). This hypothesis has been applied to explain the changes in shape of human erythrocytes that are produced by a variety of amphipathic compounds. These compounds are presumed to intercalate by their hydrophobic ends into the lipid portions of the membrane; if the compounds are anions, the binding is preferentially to the outer half of the bilayer, if cations, to the inner half. It is proposed that such preferential binding causes an expansion of one half-layer relative to the other, with a corresponding change in cell shape. The predicted sidedness of these shape changes is now demonstrated in experiments with methochlorpromazine and 2,4,6-trinitrophenol. Under appropriate nonequilibrium or equilibrium or equilibrium conditions, both of these compounds are shown to be either crenators or cup-formers of the intact erythrocyte, depending upon which side of the membrane they are concentrated in. These results therefore strongly support the bilayer couple hypothesis.

scholarly journals Fracture faces of frozen membranes: 50th anniversary

2016 ◽  
Vol 27 (3) ◽  
pp. 421-423
Author(s):  
Daniel Branton
Keyword(s):  
Electron Microscopy ◽  
Lipid Bilayers ◽  
Fracture Process ◽  
Relative Proportion ◽  
50Th Anniversary ◽  
Biological Membranes ◽  
Bilayer Membrane ◽  
Biological Cells ◽  
Membrane Surfaces ◽  
Freeze Etching

In 1961, the development of an improved freeze-etching (FE) procedure to prepare rapidly frozen biological cells or tissues for electron microscopy raised two important questions. How does a frozen cell membrane fracture? What do the extensive face views of the cell’s membranes exposed by the fracture process of FE tell us about the overall structure of biological membranes? I discovered that all frozen membranes tend to split along weakly bonded lipid bilayers. Consequently, the fracture process exposes internal membrane faces rather than either of the membrane’s two external surfaces. During etching, when ice is allowed to sublime after fracturing, limited regions of the actual membrane surfaces are revealed. Examination of the fractured faces and etched surfaces provided strong evidence that biological membranes are organized as lipid bilayers with some proteins on the surface and other proteins extending through the bilayer. Membrane splitting made it possible for electron microscopy to show the relative proportion of a membrane’s area that exists in either of these two organizational modes.

scholarly journals Modeling Membrane Curvature Generation due to Membrane–Protein Interactions

Biomolecules ◽  
2018 ◽  
Vol 8 (4) ◽  
pp. 120 ◽  
Author(s):  
Haleh Alimohamadi ◽  
Padmini Rangamani
Keyword(s):  
Membrane Proteins ◽  
Protein Interactions ◽  
Current Model ◽  
Bilayer Membrane ◽  
Membrane Curvature ◽  
Elastic Membrane ◽  
Protein Distribution ◽  
Membrane Models ◽  
Generation Mechanisms ◽  
Mathematical And Computational Modeling

To alter and adjust the shape of the plasma membrane, cells harness various mechanisms of curvature generation. Many of these curvature generation mechanisms rely on the interactions between peripheral membrane proteins, integral membrane proteins, and lipids in the bilayer membrane. Mathematical and computational modeling of membrane curvature generation has provided great insights into the physics underlying these processes. However, one of the challenges in modeling these processes is identifying the suitable constitutive relationships that describe the membrane free energy including protein distribution and curvature generation capability. Here, we review some of the commonly used continuum elastic membrane models that have been developed for this purpose and discuss their applications. Finally, we address some fundamental challenges that future theoretical methods need to overcome to push the boundaries of current model applications.

scholarly journals Overlapping function of Hrd1 and Ste24 in translocon quality control provides robust channel surveillance

2020 ◽  
Vol 295 (47) ◽  
pp. 16113-16120
Author(s):  
Avery M. Runnebohm ◽  
Kyle A. Richards ◽  
Courtney Broshar Irelan ◽  
Samantha M. Turk ◽  
Halie E. Vitali ◽  
...  
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Ubiquitin Ligase ◽  
Biological Membranes ◽  
The Other ◽  
Growth Defect ◽  
Zinc Metalloprotease

Translocation of proteins across biological membranes is essential for life. Proteins that clog the endoplasmic reticulum (ER) translocon prevent the movement of other proteins into the ER. Eukaryotes have multiple translocon quality control (TQC) mechanisms to detect and destroy proteins that persistently engage the translocon. TQC mechanisms have been defined using a limited panel of substrates that aberrantly occupy the channel. The extent of substrate overlap among TQC pathways is unknown. In this study, we found that two TQC enzymes, the ER-associated degradation ubiquitin ligase Hrd1 and zinc metalloprotease Ste24, promote degradation of characterized translocon-associated substrates of the other enzyme in Saccharomyces cerevisiae. Although both enzymes contribute to substrate turnover, our results suggest a prominent role for Hrd1 in TQC. Yeast lacking both Hrd1 and Ste24 exhibit a profound growth defect, consistent with overlapping function. Remarkably, two mutations that mildly perturb post-translational translocation and reduce the extent of aberrant translocon engagement by a model substrate diminish cellular dependence on TQC enzymes. Our data reveal previously unappreciated mechanistic complexity in TQC substrate detection and suggest that a robust translocon surveillance infrastructure maintains functional and efficient translocation machinery.

Mitochondrial permeability to chloride ion

1975 ◽  
Vol 228 (1) ◽  
pp. 122-126 ◽  
Author(s):  
MW Weiner
Keyword(s):  
Rat Liver ◽  
Chloride Transport ◽  
Biological Membranes ◽  
Chloride Ion ◽  
The Other ◽  
Beef Heart ◽  
Inner Membrane ◽  
Mitochondrial Permeability ◽  
Mitochondrial Inner Membrane ◽  
Chloride Salts

It is generally accepted that the inner membrane of the mitchondrion is not penetrated by chloride ion, in contrast to other biological membranes which are chloride permeable. In this report mitochondrial permeablity to chloride ion has been reevaluated by the measurement of passive swelling in isotonic chloride-containing solutions in the presence of an uncoupling agent. Under these conditions, mitochondria prepared from rat liver or beef heart show a definite uptake of wide variety of chloride salts. Mitochondrial chloride transport appears to be electrogenic, as is the transmembrane movement of the other halides. Therefore, the mitochondrial inner membrane shares with other biological membranes a definite permeability to this ubiquitous anion.

Influence of Electrical Stimulation on Palatability of Hot-Boned, Pre-Rigor and Cold-Boned, Post-Rigor Frozen Beef Roasts1

1982 ◽  
Vol 45 (2) ◽  
pp. 164-168 ◽  
Author(s):  
C. L. GRIFFIN ◽  
D. M. STIFFLER ◽  
E. E. RAY ◽  
B. W. BERRY
Keyword(s):  
Electrical Stimulation ◽  
Shear Force ◽  
Biceps Femoris ◽  
The Other ◽  
Biceps Femoris Muscle ◽  
Length Width ◽  
Shape Changes ◽  
Femoris Muscle ◽  
Thin Samples

The effects of electrical stimulation on palatability of hot-boned, pre-rigor and cold-boned, post-rigor frozen beef roasts were studied by use of 16 steer carcasses. Both sides of 8 carcasses were electrically stimulated (1.5 amps; 100 - 1 s impulses); sides from the other 8 carcasses served as controls. One side of each carcass was hot-boned and the remaining side was boned following a 48 h chill (2 C). Roasts from the rump portion (anterior one-fourth) of the biceps femoris muscle were vacuum-packaged and frozen (−20 C). Following a 48-h thaw (0 C). roasts were weighed, measured for length, width and depth, seasoned, placed in cooking bags and roasted to 62.5 C. Cooking losses were less (P<0.06) for hot-boned, pre-rigor frozen vs. cold-boned, post-rigor frozen roasts. Raw pH (post-freezing) was lower (P<0.01) for hot-boned than cold-boned roasts. No differences (P>0.05) were noted in shape changes for stimulation or chilling. Using triangle tests, untrained panel members were able to distinguish controls from electrically stimulated roasts and hot-boned from cold-boned roasts when served as thick (1.27 cm) or thin (2 mm) samples. Thick and thin samples of cold-boned roasts were preferred over hot-boned roasts. For roasts from carcasses that were not electrically stimulated, 62.6% preferred cold-boned roasts for thick samples while 61.4% preferred cold-boned roasts for thin samples. Cold-boned roasts from electrically stimulated carcasses were preferred over hot-boned roasts, 56.5% (thick) vs. 51.5% (thin). Warner-Bratzler shear force results indicated that hot-boned, control roasts required 79% more shear force than cold-boned roasts, but roasts from electrically stimulated carcasses required 14% more force to shear hot-boned than cold-boned roasts.

scholarly journals Localization of trehalose in partially hydrated DOPC bilayers: insights into cryoprotective mechanisms

2014 ◽  
Vol 11 (95) ◽  
pp. 20140069 ◽  
Author(s):  
Ben Kent ◽  
Taavi Hunt ◽  
Tamim A. Darwish ◽  
Thomas Hauß ◽  
Christopher J. Garvey ◽  
...  
Keyword(s):  
Experimental Data ◽  
Lipid Bilayer ◽  
Molecular Mechanisms ◽  
Biological Membranes ◽  
Water Layer ◽  
Bilayer Membrane ◽  
Lipid Bilayer Membrane ◽  
Membrane Systems ◽  
Gaussian Profile

Trehalose, a natural disaccharide with bioprotective properties, is widely recognized for its ability to preserve biological membranes during freezing and dehydration events. Despite debate over the molecular mechanisms by which this is achieved, and that different mechanisms imply quite different distributions of trehalose molecules with respect to the bilayer, there are no direct experimental data describing the location of trehalose within lipid bilayer membrane systems during dehydration. Here, we use neutron membrane diffraction to conclusively show that the trehalose distribution in a dioleoylphosphatidylcholine (DOPC) system follows a Gaussian profile centred in the water layer between bilayers. The absence of any preference for localizing near the lipid headgroups of the bilayers indicates that the bioprotective effects of trehalose at physiologically relevant concentrations are the result of non-specific mechanisms that do not rely on direct interactions with the lipid headgroups.

scholarly journals DISGORGEMENT DAMAGES FOR BREACH OF CONTRACT

2012 ◽  
Vol 20 (1) ◽  
pp. 87-110
Author(s):  
Adam Temple
Keyword(s):  
Theoretical Basis ◽  
The Other ◽  
Rational Basis ◽  
Breach Of Contract ◽  
Contractual Obligation ◽  
The Core ◽  
The Law

Gain-based damages for breach of contract are often viewed as anomalous, and lacking a clear rational basis. This article seeks to provide a theoretical basis for the requirement to disgorge profits gained through breach of contract.  By looking at the core contractual obligation, it can be seen that a contracting party has two ways in which they can fulfil their promises. They can pay damages where they fully compensate the other party, or they can perform. Where damages are inadequate, the contracting party must perform. Failure to perform in such circumstances should be prevented, and it is argued that disgorgement of profits is a suitable deterrent to such contract breakers. It is suggested that the law should act in this way to protect the facilitative institution of contract. 

scholarly journals Surface model of the human red blood cell simulating changes in membrane curvature under strain

2021 ◽  
Author(s):  
Philip W. Kuchel ◽  
Charles D. Cox ◽  
Daniel Daners ◽  
Dmitry Shishmarev ◽  
Petrik Galvosas
Keyword(s):  
Blood Cell ◽  
Red Blood Cell ◽  
Morphological Changes ◽  
Three Dimensional ◽  
Membrane Curvature ◽  
Glycolytic Flux ◽  
Surface Model ◽  
Principal Curvatures ◽  
Quartic Equation ◽  
Shape Changes

Abstract The highly deformable red blood cell (erythrocyte; RBC) responds to mechanically imposed shape changes with enhanced glycolytic flux and cation transport. Such morphological changes are produced experimentally by suspending the cells in a gelatin gel, which is then elongated or compressed in a special apparatus inside an NMR spectrometer. However, direct mathematical predictions of the shapes of the morphed cells have not been reported before. We used recently available functions in Mathematica to triangularize and then compute four types of curvature. The RBCs were described by a previously presented quartic equation in three dimensional (3D) Cartesian space. A key finding was the extent to which the maximum and minimum Principal Curvatures were localized symmetrically in patches at the poles or equators and distributed in rings around the main axis of the strained RBC. The simulations, on the nano-metre to micro-meter scale of curvature, suggest activation of only a subset of the intrinsic mechanosensitive cation channels, Piezo1, during experiments carried out with controlled distortions that persist for many hours. This view is consistent with a recent proposal for non-uniform distribution of Piezo1 molecules around the RBC membrane. On the other hand, if the curvature that gates Piezo1 is at a much finer length scale, then membrane tension will determine local curvature and micron scale curvature as described here will be less likely to influence Piezo1 activity. The geometrical reorganization of the simulated cytoskeleton helps understanding of the concerted metabolic and cation-flux responses of the RBC to mechanically imposed shape changes.

scholarly journals SINAL DOS TEMPOS: O AMBIENTE DA ORGANIZAÇÃO QUE TRANSCENDE

2016 ◽  
Vol 23 (2) ◽  
pp. 214
Author(s):  
Jonas Fernando Petry ◽  
Marcia Zanievicz da Silva ◽  
Denise Del Prá Netto Machado
Keyword(s):  
Public Policy ◽  
Organizational Ecology ◽  
The Other ◽  
Rational Basis ◽  
Interconnected System ◽  
Healthy Environment ◽  
Decision Aiding ◽  
Per Capita ◽  
Geographical Context ◽  
The Ideal

RESUMO Objetiva-se a integração sob a perspectiva ecológica e contingencial da relação organização/ambiente e a mensuração das 37 cidades brasileiras detentoras de economia e ambiente saudáveis, por meio de uma análise baseada no Apoio Multicritério à Decisão (AMD). O objetivo concentra-se em medir o desempenho das cidades a partir de um conjunto de variáveis com abordagens contingenciais e ecológicas, a fim de verificar o esforço de adaptação das cidades, permitindo identificar e comparar quais cidades podem apresentar melhor relação organização/ambiente dentro de um contexto geográfico. Para isso, baseia-se nas possibilidades contidas nos métodos de AMD: Displaced Ideal e TOPSIS. A pesquisa é caracterizada como descritiva, visto que visa ranquear 37 cidades brasileiras. Os resultados mostram que o número de empresas, a renda per capita e o IDH exercem papel importantíssimo sobre as demais variáveis. Entende-se que a avaliação da relação organização vs ambiente é um imenso sistema interligado que depende da eficiência no uso dos recursos para implicar eficácia no ambiente ideal. Assim, aumento no número de empresas representa melhora do IDH e reclama maiores gastos com outras variáveis. O conjunto de variáveis requer esforço e é a base racional eficaz para direcionar políticas públicas. Palavras-chave: Ecologia Organizacional. Teoria da Contingência. Ambientes das Organizações. ABSTRACT This study attempts to integrate two approaches regarding the organization versus the environment and the measurement of 37 Brazilian cities that have both a healthy economy and a healthy environment, through na approach based on Multi Criteria Decision Aiding (MCDA) analysis. Its goal is to measure the performance of the cities based on a set of variables with contingency and ecological approaches, in order to measure the effort to adapt the cities, enabling us to identify and compare which cities have a better organization versus environment relationship, within a specific geographical context. It is based on the possibilities contained in the MCDA methods: Displaced Ideal and TOPSIS (American School). In terms of its goals, the research is characterized as descriptive, as it seeks to rank 37 Brazilian cities. The results show that the number of companies, per capita ncome, and HDI have a significant effect on the other variables. the evaluation of the organization versus environment relationship is seen as a vast, interconnected system that depends on the efficient use of the resources to bring effectiveness in the ideal environment. Thus, an increase in the number of businesses represents an improvement in the HDI and requires increased spending on other variables. The set of variables requires effort and is the effective rational basis for guiding public policy. Keywords: Organizational Ecology. Contingency Theory. Organization Environments.

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