Biological membranes study

With the adequacy of lipid bilayer membranes as models for the basic structural motif and hence for the ion transport barrier of biological membranes, studies of channel and carrier ion transport mechanisms across such membranes become of central relevance to transport across cell membranes. The fundamental principles derived from these studies, however, have generality beyond the specific model systems. As noted above and as will be treated below, it is found that selective transport... 

Zachariasse K. A., Kozankiewicz B. and Kuhnle W. (1983) Micelles and Biological Membranes Studied by Probe Molecules, in Zewail A. H. (Ed.), Photochemistry and Photobiology, Vol. II, Harwood, London, pp. 941-960. 

J.-M. Bassot, in "Recent Advances in Biological Membrane Studies , L. Packer, Editor. (1985), Plenum New York. pp. 259-284. 

Fitter J, Lechner RE, Dencher NA Interactions of hydration water and biological membranes studied by neutron scattering. J. Phys. Chem. B 1999,103 8036-8050. 

Vesicles, bicelles and L.C. dispersions. The large number of papers devoted to vesicle and bicelle formulations reflects the paramount importance they have in both applied and theoretical field. As for the above paragraph such aggregates has often been used to stabilize membrane protein and peptides to be studied. Furthermore because of their supra-molecular architecture, they represent the most common fluid nanocontainers for drug delivery applications and the most common mimicking systems in biological membranes studies. 

Volume 97—Recent Advances in Biological Membrane Studies Structure and Biogenesis, Oxidation and Energetics edited by Lester Packer... 

The study of mixed films has become of considerable interest. From the theoretical side, there are pleasing extensions of the various models for single-component films and from the more empirical side, one moves closer to modeling biological membranes. Following Gershfeld [200], we categorize systems as follows ... 

Biological membranes provide the essential barrier between cells and the organelles of which cells are composed. Cellular membranes are complicated extensive biomolecular sheetlike structures, mostly fonned by lipid molecules held together by cooperative nonco-valent interactions. A membrane is not a static structure, but rather a complex dynamical two-dimensional liquid crystalline fluid mosaic of oriented proteins and lipids. A number of experimental approaches can be used to investigate and characterize biological membranes. However, the complexity of membranes is such that experimental data remain very difficult to interpret at the microscopic level. In recent years, computational studies of membranes based on detailed atomic models, as summarized in Chapter 21, have greatly increased the ability to interpret experimental data, yielding a much-improved picture of the structure and dynamics of lipid bilayers and the relationship of those properties to membrane function [21]. 

Langmuir-Blodgett films (LB) and self assembled monolayers (SAM) deposited on metal surfaces have been studied by SERS spectroscopy in several investigations. For example, mono- and bilayers of phospholipids and cholesterol deposited on a rutile prism with a silver coating have been analyzed in contact with water. The study showed that in these models of biological membranes the second layer modified the fluidity of the first monolayer, and revealed the conformation of the polar head close to the silver [4.300]. 

Ion-selective bulk membranes are the electro-active component of ion-selective electrodes. They differ from biological membranes in many aspects, the most marked being their thickness which is normally more then 105 times greater, therefore electroneutrality exists in the interior. A further difference is given by the fact that ion-selective membranes are homogeneous and symmetric with respect to their functioning. However, because of certain similarities with biomembranes (e.g., ion-selectivity order, etc.) the more easily to handle ion-selective membranes were studied extensively also by many physiologists and biochemists as model membranes. For this reason research in the field of bio-membranes, and developments in the field of ion-selective electrodes have been of mutual benefit. 

To obtain an increased intrinsic capacity to transgress biological membranes, a number of different modifications have been introduced to PNA. These modifications include conjugation of PNA to Hpophilic moieties [51, 97, 98], conjugation of PNA to certain so-caUed ceU-penetrating peptides [49, 55, 56, 66, 99-102] and conjugation to different moieties, which are supposed to be internahzed by specific cellular receptors [48, 103-105]. The work on cellular dehvery of PNA is, like the related work on ex vivo and in vivo effects of PNA, very difficult to summarize conclusively. First of all, the pronounced diversity of the reporter systems employed makes it impossible to directly compare the studies. Secondly, the widespread use of fluorescence studies in spite of the many inherent pitfalls of this technique makes it sometimes difficult to judge even qualitatively whether a presented result actually indicates cellular uptake. We have recently published a comprehensive review on cellular dehvery of PNA [82], with a more detailed assessment of the PNA dehvery hterature. 

The use of Upid bilayers as a relevant model of biological membranes has provided important information on the structure and function of cell membranes. To utilize the function of cell membrane components for practical applications, a stabilization of Upid bilayers is imperative, because free-standing bilayer lipid membranes (BLMs) typically survive for minutes to hours and are very sensitive to vibration and mechanical shocks [156,157]. The following concept introduces S-layer proteins as supporting structures for BLMs (Fig. 15c) with largely retained physical features (e.g., thickness of the bilayer, fluidity). Electrophysical and spectroscopical studies have been performed to assess the appUcation potential of S-layer-supported lipid membranes. The S-layer protein used in aU studies on planar BLMs was isolated fromB. coagulans E38/vl. 

In concluding this section we hope we have shown that there is a clear need for more elaborated studies to understand how lipophilic ions interact with biological membranes - an aspect that may look deceptively simple, but which is not yet completely understood. 

Koryta et al. [48] first stressed the relevance of adsorbed phospholipid monolayers at the ITIES for clarification of biological membrane phenomena. Girault and Schiffrin [49] first attempted to characterize quantitatively the monolayers of phosphatidylcholine and phos-phatidylethanolamine at the ideally polarized water-1,2-dichloroethane interface with electrocapillary measurements. The results obtained indicate the importance of the surface pH in the ionization of the amino group of phosphatidylethanolamine. Kakiuchi et al. [50] used the video-image method to study the conditions for obtaining electrocapillary curves of the dilauroylphosphatidylcholine monolayer formed on the ideally polarized water-nitrobenzene interface. This phospholipid was found to lower markedly the surface tension by forming a stable monolayer when the interface was polarized so that the aqueous phase had a negative potential with respect to the nitrobenzene phase [50,51] (cf. Fig. 5). 

The protein-containing colloidal solutions of water-in-organic solvents are optically transparent. Hence, absorption spectroscopy, circular dichroism spectroscopy and fluorescence spectroscopy are found to be convenient for studying biocatalysis [53]. The reversed micelles are interesting models for studying bioconversion, since the majority of the enzymes in vivo act inside or on the surface of biological membranes. 

Various types of research are carried out on ITIESs nowadays. These studies are modeled on electrochemical techniques, theories, and systems. Studies of ion transfer across ITIESs are especially interesting and important because these are the only studies on ITIESs. Many complex ion transfers assisted by some chemical reactions have been studied, to say nothing of single ion transfers. In the world of nature, many types of ion transfer play important roles such as selective ion transfer through biological membranes. Therefore, there are quite a few studies that get ideas from those systems, while many interests from analytical applications motivate those too. Since the ion transfer at an ITIES is closely related with the fields of solvent extraction and ion-selective electrodes, these studies mainly deal with facilitated ion transfer by various kinds of ionophores. Since crown ethers as ionophores show interesting selectivity, a lot of derivatives are synthesized and their selectivities are evaluated in solvent extraction, ion-selective systems, etc. Of course electrochemical studies on ITIESs are also suitable for the systems of ion transfer facilitated by crown ethers and have thrown new light on the mechanisms of selectivity exhibited by crown ethers. 

Whereas the relationship of solute permeability with lipophilicity has been studied in a large number of in vivo systems (including intestinal absorption models [54,55], blood-brain [56 58] and blood nerve [59] barrier models, and cell culture models [60 62], to name just a few), numerous in vitro model systems have been developed to overcome the complexity of working with biological membranes [63-66]. Apart from oil-water systems that are discussed here, the distribution of a solute between a water phase and liposomes is... 

There are no convenient databases for liposome log P values. Most measured quantities need to be ferreted from original publications [149,162,376,381-387,443], The handbook edited by Cevc [380] is a comprehensive collection of properties of phospholipids, including extensive compilations of structural data from X-ray crystallographic studies. Lipid-type distributions in various biological membranes have been reported [380,388,433]. 

The discovery of galvanic electricity (i.e. electrical phenomena connected with the passage of electric current) by L. Galvani in 1786 occurred simultaneously with his study of a bioelectrochemical phenomenon which was the response of excitable tissue to an electric impulse. E. du Bois-Reymond found in 1849 that such electrical phenomena occur at the surface of the tissue, but it was not until almost half a century later that W. Ostwald demonstrated that the site of these processes are electrochemical semipermeable membranes. In the next decade, research on semipermeable membranes progressed in two directions—in the search for models of biological membranes and in the study of actual biological membranes. 

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