摘要:

AbstractModel membrane systems are used extensively in all aspects of membrane research, and freeze‐fracture is the preeminent procedure for directly visualizing local structure in these lipid dispersions. Here we describe in detail the formation of liposomes and how freeze‐fracture is routinely employed as a complementary technique to biophysical and biochemical procedures in the characterization of multilamellar vesicles (most commonly known as liposomes) and unilamellar vesicles. Many preparative procedures exist for the formation of multi‐ and unilamellar vesicles. Examples of each system are given and their properties as well as freeze‐fracture morphology are discussed. The detection of lipid‐phase transitions is considered, in particular, with emphasis on the application of freeze‐fracture to the study of lipid polymorphism. We briefly discuss the fracturing of apolar lipids which do not adopt bilayer structures but which can be stabilized into microemulsions by a phospholipid monolayer. Finally, a critical assessment is made of filipin as a morphological marker for cholesterol domains in the plane of

ISSN:0741-0581    

DOI:10.1002/jemt.1060130403

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThe use of whole, intact plant tissue for freeze‐fracture electron microscopy provides important information that cannot be obtained from the use of isolated biological membranes or of artifical (phospholipid) membrane preparations. This is not to imply that these exminations of such preparations are not useful, since it would be difficult to interpret our observations of intact cells and tissues without the analysis of these model systems. Analysis of intact tissue and cells reveals the relative densities of membrane proteins of the different membranes within a cell; the three‐dimensional organization of various organelles, especially the endoplasmic reticulum; changes in intramembranous particle (IMP) distribution due to stress or injury; and, in conjunction with the use of filipin, membrane sterol content and relative distribution.It is our intention that this survey of freeze‐fracture images of intact plant tissues will illustrate the uniqueness of the information gained from an analysis of whole plant tissues compared to isolated membrane frac

ISSN:0741-0581    

DOI:10.1002/jemt.1060130404

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractManufacture of food products with desired texture and stability increasingly benefits from an understanding of the food microstructure. Freeze‐fracture is advantageous in gaining this understanding because it avoids alterations of hydration, retains fat, and maximally preserves air cells. This paper reviews insightful applications of freeze‐fracture to various food crystals, colloids, gels, emulsions, and fo

ISSN:0741-0581    

DOI:10.1002/jemt.1060130405

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractUnderstanding the relationship between the molecular structure and the macroscopic properties of polymer solutions and gels, oil‐water‐surfactant emulsions, lyotropic and thermotropic liquid crystals, colloidal dispersions, detergents, and other such “microstructured fluids” is essential to the optimal use of these commercially important materials. Modern rapid‐freezing methods followed by freeze‐fracture replication techniques are ideally suited to allow the direct visualization of the three‐dimensional structure of the particles or units that make up the dispersion, while simultaneously revealing their orientation and distribution with molecular resolution. This paper reviews the necessary experimental conditions required to successfully exploit the freeze‐fracture technique as it applies to microstructured fluid systems. The benefits and limitations of structural studies by freeze‐fracture techniques as opposed to the more commonly used light, X‐ray, and neutron‐scattering methods are discussed. Freeze‐fracture replicas can also be imaged by scanning tunneling microscopy to reveal directly three‐dimensional fracture contours

ISSN:0741-0581    

DOI:10.1002/jemt.1060130406

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractSingle molecule resolution in beam‐sensitive, uncoated, noncrystalline materials has heretofore not been possible except in thin (≤150 Å) platinum‐carbon (Pt‐C) replicas, which are resistant to electron beam destruction. Previously, the granularity of metal film replicas limited their resolution to ≥20 Å. This paper demonstrates that Pt‐C film granularity and resolution are a function of the method of replication and other controllable factors. Low‐angle 20° rotary, 45° unidirectional, and vertical 9.7 ± 1 Å Pt‐C films deposited on mica under the same conditions were compared. Vertical replication had a 5 Å granularity, the highest resolution, and evenly coated the whole surface. A 45° replication had a 9.5 Å granularity, a slightly poorer resolution, and a discontinuous surface coating. The use of 20° rotary replication proved to be unsuitable for high‐resolution imaging, with 20–25 Å granularity and resolution two to three times poorer. Vertical and 45° Pt‐C replicas can visualize the deep‐etched DNA helix and the 13.3 Å 32helix of pectin in a gel. The DNA double helix, the complex structures of sol‐gel glasses, Immobilon filters (polyvinylidene fluoride), a polymethacrylate plastic, the metal oxide surfaces of 440c stainless steel, and aluminum are illustrated. This high‐resolution vertical Pt‐C replica technique can image in the context of solutions, gels, or solids, single molecular chains 3–7 Å wide, their associations, and their conformation. Included in the present article are first time descriptions for removing replicas from metals and plastics and for making high‐magnification photographic prints of normal c

ISSN:0741-0581    

DOI:10.1002/jemt.1060130407

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThis article reviews research on planar monolayer methods, application of the methods to analyses of transmembrane signaling, and the combination of these methods with scanning tunneling microscopy (STM). Past research has involved the development of monolayer freeze‐fracture methods. These include monolayer freeze‐fracture autoradiography (MONOFARG), an electron microscopic cytochemical method to analyze in‐plane distributions of radioisotopes, and double‐labeled membrane splitting (DBLAMS) and single‐membrane monolayer splitting (SMMS), methods to analyze transmembrane distributions of native and radiolabeled proteins and lipids. Present research has focussed on using these methods to investigate mechanisms of transmembrane signaling mediated by protein kinase C (PKC), including the transbilayer distribution of the tumor promoter TPA, a lipophilic activator of PKC, and the transbilayer distribution of peripheral membrane proteins phosphorylated by PKC. Future work will involve the combination of planar sample preparation with STM. The principles and applications of biological STM are briefly reviewed and a low‐resolution STM image of a planar purple‐membrane monolayer is included. The combination of planar methods and STM can provide the chemical information lacking in STM images enabling microscopists to investigate biochemical phenomena at nanomet

ISSN:0741-0581    

DOI:10.1002/jemt.1060130408

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

ISSN:0741-0581    

DOI:10.1002/jemt.1060130409

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

ISSN:0741-0581    

DOI:10.1002/jemt.1060130410

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

ISSN:0741-0581    

DOI:10.1002/jemt.1060130411

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

ISSN:0741-0581    

DOI:10.1002/jemt.1060130402

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY