摘要:

The isolated plasma membrane of the human erythrocytes displays the same shape and shape transformations as the intact cells. It is therefore generally believed that the plasma membrane plays a dominant role in determining erythrocyte shape. The plasma membrane consists of a fluid lipid bilayer to the surface of which is attached a protein skeleton. The two halves of the lipid bilayer and the protein network (gel) are tighly coupled, but at the same time elastically deformable and can slide relative to one another in the plane of the cell membrane. The equilibrium shape of such a structure is determined by the combined mechano‐chemical properties of the individual layers and equals the cell shape that for the given cell volume corresponds to the lowest total elastic free energy. The elastic free energy of the lipid bilayer is mainly associated with bending and change in surface area for each of the two lipid monolayer. For the protein membrane skeleton the elastic free energy mainly equals the sum of the local contributions due to shear deformation and surface change. When the mechano‐chemical properties of each of the layers are known, calculation of the equilibrium shape is in principle just an exercise in standard continuum mechanics. The elastic properties of pure lipid monolayers have long been qualitatively fairly well known. The changes in lipid bilayer elastic properties resulting from the presence of integral membrane proteins have just recently become better understood. The detailed molecular basis for the elastic properties of the protein membrane skeleton remains unresolved despite many attempts to elucidate the problem. It is widely agreed that the elastic properties are largely accounted for by the highly elongated spectrin molecules, but whether the membrane skelton elasticity is mainly of entropic or entalphic origin is still unsettled.

ISSN:0094-243X    

DOI:10.1063/1.40603

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Spectrin, &agr;‐actinin and dystrophin make up a closely related group, termed spectrin superfamily. We have carried out a preliminary analysis of the repeating amino acid sequences in the rod‐shaped domains of these proteins and made use of structural constraints imposed by &agr;‐helical coiled‐coil‐like packing. We show that the common conformation of these repeats may be described four‐&agr;‐helix motif found in many globular proteins.

ISSN:0094-243X    

DOI:10.1063/1.40604

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The effect of ioxitalamate, a radiological contrast medium, on red blood cell (RBC) elastic properties has been studied. Individual red blood cells are gently aspirated by an accurately controlled pressure into the tip of a glass micropipette. Cells are deformed with a well‐defined force produced by a very small suction pressure. An elasticity shear modulus is then deduced.At a concentration isoosmotic to plasma, the elasticity shear modulus remains normal. At a concentration hyperosmotic to plasma the elasticity shear modulus is significantly higher than the one obtained for cells suspended in either isoosmotic or hyperosmotic buffer.It can be concluded that the effect of ioxitalamate at a volume ratio of 20% on elastic properties of RBC is related to membrane changes and not to the increase in osmolality.

ISSN:0094-243X    

DOI:10.1063/1.40605

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

After microinjection into cultured Vero cells, rhodamine‐labeled clathrin triskelions gave rise to a punctuate fluorescence pattern typical for clathrin, with two major localizations: the plasma membrane and the perinuclear region of the cells. We analyzed clathrin motion by Fluorescence Recovery After Photobleaching and its 3 dimensional distribution by Confocal Microscopy. Altogether, 55% of total clathrin is polymerized into coats which are turning over with a half time of 11 seconds and 45% of total diffuses freely in the cytoplasm. Various conditions known to affect membrane traffic were investigated. Cytosolic acidification or ATP depletion stabilized the polymerized clathrin coats without modifying the ratio of free versus polymerized clathrin. Low temperature (6 °C) or hypertonic media dramatically increased both the stability and the amount of the polymerized clathrin. We conclude that ATP and pH homeostasis are needed to support a very high turnover of the clathrin coats in living cells whereas low temperature and high osmotic strength promote an extensive polymerization of clathrin.

ISSN:0094-243X    

DOI:10.1063/1.40607

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We labelled endocytic veiscles of living Mouse Fibroblasts Clone 1D, by incubating the cells in their culture medium containing Rhodamine‐Dextranes (RD). Microfluorimetric measurements showed that RD was internalized by pinocytosis. FRAP curves determined at 17 °C on cells incubated with RD showed that there were three classes of vesicles: quick moving vesicles, slow moving vesicles and immobile vesicles. The times t1and t2of fluorescence half recovery of the two mobile vesicule classes were proportional to the laser beam radius. The FRAP curves were considered as resulting from the flow of vesicles whose velocities were distributed according to a bimodal gaussian function. The average velocities depended on the incubation time and varied between 6 to 11 &mgr;m sec−1for V¯1and 0.3 to 0.7 &mgr;m sec−1for V¯2. This last velocity was ascribed to the saltatory motion of lysosomes and endosomes while V¯1was considered to represent the velocity of small vesicles which have not been detected so far by optical microscopy.

ISSN:0094-243X    

DOI:10.1063/1.40562

出版商:AIP    

年代:1991

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.40563

出版商:AIP    

年代:1991

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.40564

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We present examples of measurements of dynamic properties of various surfactant systems (monolayers, lamellar phases, tubular micelles) whose microstructure presents similarities with those of the cytoskeleton elements. The measurements are done with several optical techniques: surface light scattering, excited surface devices, quasielastic bulk light scattering and fluorescence recovery after fringe pattern photobleaching. They allow one to obtain information on diffusion processes and on the viscoelastic behavior of the surfactant systems. The importance of the characteristic frequency of the measurement is discussed.

ISSN:0094-243X    

DOI:10.1063/1.40565

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Shape changes of giant liposomes are triggered by small variations of the number of lipids on either side of the liposome membrane. Thus, the bilayer couple hypothesis applies even in a protein free system.

ISSN:0094-243X    

DOI:10.1063/1.40566

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A method for orienting long chain biopolymers and the advantages for interpreting the structure using x‐rays is discussed. Three examples of microbial polysaccharides are used to illustrate the application of x‐ray diffraction to oriented films.

ISSN:0094-243X    

DOI:10.1063/1.40567

出版商:AIP    

年代:1991

数据来源: AIP