Biomembranes model systems

R. A. Dluhy, S.M. Stephens, S. Widayatl and A.D. Williams, Vibrational Spectroscopy of Biophysical Monolayers. Applications of IR and Raman Spectroscopy to Biomembrane Model Systems at Interfaces, Spectrochim. Acta Part A51 (1995) 1413. (Review on biomembrane model systems studied by surface-sensitive vibrational spectroscopic methods. In particular the following methods are surveyed external reflectance IR spectroscopy, wave-guide Raman spectroscopy cmd SERS.)... 

Antoloni, R., Gliozzi, A. and Gorio, A. (eds) (1982) Transport in Biomembranes Model Systems and Reconstitution, New York Raven Press. 

There is quite a large body of literature on films of biological substances and related model compounds, much of it made possible by the sophisticated microscopic techniques discussed in Section IV-3E. There is considerable interest in biomembranes and how they can be modeled by lipid monolayers [35]. In this section we briefly discuss lipid monolayers, lipolytic enzyme reactions, and model systems for studies of biological recognition. The related subjects of membranes and vesicles are covered in the following section. 

Lipophilicity is intuitively felt to be a key parameter in predicting and interpreting permeability and thus the number of types of lipophilicity systems under study has grown enormously over the years to increase the chances of finding good mimics of biomembrane models. However, the relationship between lipophilicity descriptors and the membrane permeation process is not clear. Membrane permeation is due to two main components the partition rate constant between the lipid leaflet and the aqueous environment and the flip-flop rate constant between the two lipid leaflets in the bilayer [13]. Since the flip-flop is supposed to be rate limiting in the permeation process, permeation is determined by the partition coefficient between the lipid and the aqueous phase (which can easily be determined by log D) and the flip-flop rate constant, which may or may not depend on lipophilicity and if it does so depend, on which lipophilicity scale should it be based ... 

Thus far, it could be shown that stable liposomes can be prepared by polymerization of lipids. These vesicle systems, however, are still far away from being a real biomembrane model. As of now, they do not show any typical biological behavior such as surface recognition, enzymatic activities, variable lipid distribution, and the ability to undergo fusion. 

There are two ways different in principle, to approach the problem of creating a polymeric biomembrane model. One can start out from a completely synthetic system and increase the similarity to natural systems by introducing natural lipids and... 

Order and Mobility are two basic principles of mother nature. The two extremes are realized in the perfect order of crystals with their lack of mobility and in the high mobility of liquids and their lack of order. Both properties are combined in liquid crystalline phases based on the selforganization of formanisotropic molecules. Their importance became more and more visible during the last years in Material science they are a basis of new materials, in Life science they are important for many structure associated functions of biological systems. The main contribution of Polymer science to thermotropic and lyotropic liquid crystals as well as to biomembrane models consists in the fact that macromolecules can stabilize organized systems and at the same time retain mobility. The synthesis, structure, properties and phototunctionalization of polymeric amphiphiles in monolayers and multilayers will be discussed. 

Artificial biomembrane mimetic model systems are used to characterize peptide-membrane interactions using a wide range of methods. Herein, we present the use of selected membrane model systems to investigate peptide-membrane interactions. We describe methods for the preparation of various membrane mimetic media. Our applications will focus on small unilamellar vesicles (SUVs) and large unilamellar vesicles (LUVs) as well as on media more suited for nuclear magnetic resonance (NMR) techniques, micelles, and fast-tumbling two-component bilayered micelles (bicelles). 

Mabrey S, Sturtevant JM. High-sensitivity differential scanning calorimetry in the study of biomembranes and related model systems. In Methods in Membrane Biology. Korn EDE, ed. 1978. Plenium Press, New York. pp. 237-274. 

In this paper, we examine the Interactions of pyran copolymer with model biomembranes of two kinds 1) the human red blood cell membrane (or red cell "ghost") and 11) multilamellar suspensions (liposomes) of dlpalmltoylphosphatldylchollne (DFPC), a pure synthetic phospholipid. Each of these systems offers advantages In studies of polymer-cell surface Interaction The red cell membrane, idille complex. Is still the most readily Isolated and best understood of the membranes of nonnal human cells, and Its molecular architecture Is, In a general way at least, typical of such membranes. The pure phospholipids provide a much simpler biomembrane model, with the prospect of yielding more complete Interpretation of experimental observations. 

This model system studies the antioxidant potential against the attack of oxygen radicals on biomembranes from aqueous phase [52]. Antioxidant effects of olive phenols depend on their interaction with model membranes [53], e.g., oleuropein interacts with DMPC (dimyristoyl-phosphatidyl-choline) membranes. Oleuropein contains a sugar moiety needed to prevent drug access to lipid membranes [54]. In... 

A biological membrane is a structure particularly suitable for study by the LB technique. The eukaryotic cell membrane is a barrier that serves as a highway and controls the transfer of important molecules in and out of the cell (Roth etal., 2000). The cell membrane consists of a bilayer or a two-layer LB film (Tien etal, 1998). Lipid bilayers are composed of a variety of amphiphilic molecules, mainly phospholipids and sterols which in turn consist of a hydrophobic tail, and a hydrophilic headgroup. The complexity of the biomembrane is such that frequently simpler systems are used as models for physical investigations. They are based on the spontaneous self-organization of the amphiphilic lipid molecules when brought in contact with an aqueous medium. The three most frequently used model systems are monolayers, black lipid membranes, and vesicles or liposomes. 

Model systems range from the unique water structures at solid surfaces and water shells around proteins and biomembranes, via amino and nucleic acids, proteins, DNA, phospholipid membranes, to cells and living tissue at surfaces. At one end of the spectrum the scientific challenge is to map out the structures, bonding, dynamics and kinetics of biomolecules at surfaces in a similar way as has been done for simple molecules during the past three decades in surface science. At the other end of the complexity spectrum one addresses how biofunctional surfaces participate in and can be designed to constructively participate in the total communication system of cells and tissue. ... 

The remaining discussion in this section is devoted to the examination of various models and model systems that have been developed in attempts to characterize, in terms of physical and chemical mechanisms, the response of a biomembrane to weak electromagnetic fields. The role and utility of modeling is often misunderstood, and thus a brief explanation is in order here. Models have proved to be an important component in methods that have been successfully employed as deductively manipulative constructs essential to the evolution of theory from observation. As such, they should serve as supplements to experimentation by suggesting new experiments. As well, they should possess the obvious capability of explaining existing experimental observations. 

Because of its occurence in diseased tissue, the mode of association of cholesterol esters with biomembranes is of interest. Possible modes of association could be droplets within the hydrophobic core of the membrane bilayer, binding to membrane protein or as part of membrane attached serum lipoproteins. A potentially useful model system for investigating this association is the membrane of the microorganism Mycoplasma capricolum. The Mycoplasma due to their simplicity have served as model membrane systems in many studies. As mentioned previously, cholesterol esters show complex behavior that is a function of thermal history, impurities and physical packing constraints. Using DSC on native membranes and extracted membrane material, it was possible to demonstrate that the majority of cholesterol esters associated with the membranes of M. capricolum exist as relatively large and pure liquid droplets (17). 

A model system which is most useful is a dispersion of a pure phospholipid in water or in aqueous buffer, prepared with vigorous mechanical agitation. Under these conditions, phospholipids form "multilamellar suspensions," sometimes called "liposomes," which consist of concentric spherical lipid bilayers separated from one another by excess water. The assumption is that one can gain some understanding of the lipid bilayer component of natural biomembranes through the study of these simpler molecular systems. 

Owing to complex structural and environmental factors associated with biomembranes, numerous investigators used different techniques and carried out studies on model systems in order to understand the fundamental life processes. These include ion accumulation or active transport, conduction of nerve impulses, energy transduction, protein synthesis, permeability barrier of ions and molecules, immunological reactions, phagocytosis and pinocytosis, and so on, in physical and chemical terms [3]. Under separate headings below, different model systems will be described. 

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