Phospholipid biomembrane

Pignatello R, Toth I, Puglisi G (2001) Structural effects of lipophilic methotrexate conjugates on model phospholipid biomembranes. Thermochim. Acta 380 255-264. 

Organized adsorption layer of phospholipids (Biomembrane-Iike surface)... 

Figure 10 Generalized phospholipid biomembrane showing inclusion of a pore.

Although extraction of lipids from membranes can be induced in atomic force apparatus (Leckband et al., 1994) and biomembrane force probe (Evans et al., 1991) experiments, spontaneous dissociation of a lipid from a membrane occurs very rarely because it involves an energy barrier of about 20 kcal/mol (Cevc and Marsh, 1987). However, lipids are known to be extracted from membranes by various enzymes. One such enzyme is phospholipase A2 (PLA2), which complexes with membrane surfaces, destabilizes a phospholipid, extracts it from the membrane, and catalyzes the hydrolysis reaction of the srir2-acyl chain of the lipid, producing lysophospholipids and fatty acids (Slotboom et al., 1982 Dennis, 1983 Jain et al., 1995). SMD simulations were employed to investigate the extraction of a lipid molecule from a DLPE monolayer by human synovial PLA2 (see Eig. 6b), and to compare this process to the extraction of a lipid from a lipid monolayer into the aqueous phase (Stepaniants et al., 1997). 

A typical biomembrane consists largely of amphiphilic lipids with small hydrophilic head groups and long hydrophobic fatty acid tails. These amphiphiles are insoluble in water (<10 ° mol L ) and capable of self-organization into uitrathin bilaycr lipid membranes (BLMs). Until 1977 only natural lipids, in particular phospholipids like lecithins, were believed to form spherical and related vesicular membrane structures. Intricate interactions of the head groups were supposed to be necessary for the self-organization of several ten thousands of... 

Biomembranes mainly consists of phospholipid matrices, and the major component is phosphorylcholines (PC). PC is an amphiphile consisting of hydrophilic headgroup and hydrophobic long chains. In view of the amphiphilic feature of PC, we can divide hydrated lipid bilayers into the three zones, I, II, and III. The zone model, which has been used in a recent NMR study of DD [46-48], is illustrated in Fig. 2. 

As an example of suspected endocrine disruptors (EDs), studies of the estrogenic action of bisphenol A (BPA) have been in progress in medical, physiological, and biological fields. In this situation, physicochemical approaches are required to get the structural information of BPA trapped in biomembranes. Most recently, we have determined the site and the orientation of BPA trapped in phospholipid vesicles by NMR, using the HCS rule [47]. In particular, we have succeeded in monitoring the NMR spectral changes of phospholipid vesicles, which are induced by the BPA delivery. 

Transversely, mammalian biomembranes exhibit a general pattern for preferential localization of choline-containing phospholipids [such as phosphatidylcholine (PC) and... 

Liposomes are formed due to the amphiphilic character of lipids which assemble into bilayers by the force of hydrophobic interaction. Similar assemblies of lipids form microspheres when neutral lipids, such as triglycerides, are dispersed with phospholipids. Liposomes are conventionally classified into three groups by their morphology, i.e., multilamellar vesicle (MLV), small unilamellar vesicle (SUV), and large unilamellar vesicle (LUV). This classification of liposomes is useful when liposomes are used as models for biomembranes. However, when liposomes are used as capsules for drugs, size and homogeneity of the liposomes are more important than the number of lamellars in a liposome. Therefore, "sized" liposomes are preferred. These are prepared by extrusion through a polycarbonate... 

Compound lipids (phospholipids, sphingolipids, glycolipids, and cholesterol and its esters) that make part of the biomembrane are subject to a less active renew-al as compared with triacylglycerides. Their renewal is associated either with the restoration of an impaired portion of the membrane, or with the replacement of a defective molecule by a new one. 

Abstract To understand how membrane-active peptides (MAPs) function in vivo, it is essential to obtain structural information about them in their membrane-bound state. Most biophysical approaches rely on the use of bilayers prepared from synthetic phospholipids, i.e. artificial model membranes. A particularly successful structural method is solid-state NMR, which makes use of macroscopically oriented lipid bilayers to study selectively isotope-labelled peptides. Native biomembranes, however, have a far more complex lipid composition and a significant non-lipidic content (protein and carbohydrate). Model membranes, therefore, are not really adequate to address questions concerning for example the selectivity of these membranolytic peptides against prokaryotic vs eukaryotic cells, their varying activities against different bacterial strains, or other related biological issues. 

Figure 16 shows the experimental arrangement for the measurement of the surface pressure. The trough (200 mm long, 50 mm wide and 10 mm deep) was coated with Teflon. The subphase temperature was controlled within 0.1 C by means of a jacket connected to a thermostated water circulator, and the environmental air temperature was kept at 18 °C. The surface tension was measured with a Wilhelmy plate of platinum(24.5 x 10.0 x 0.15 mm). The surface pressure monitored by an electronic balance was successively stored in a micro- computer, and then Fourier transformed to a frequency domain. The surface area was changed successively in a sinusoidal manner, between 37.5 A2/molecule and 62.5 A2/molecule. We have chosen an unsaturated phospholipid(l,2-dioleoyl-3-sn-phosphatidyI-choline DOPC) as a curious sample to measure the dynamic surface tension with this novel instrument, as the unsaturated lipids play an important role in biomembranes and, moreover, such a "fluid" lipid was expected to exhibit marked dynamic, nonlinear characteristics. The spreading solution was 0.133 mM chloroform solution of DOPC. The chloroform was purified with three consecutive distillations. 

In the fluid state, the lateral diffusion coefficient of lipids in the bilayer structure is 0( 10 1 ) m2 s-1 (the symbol O is used to indicate order of magnitude). Interestingly, it has been shown that the diffusion coefficients of phospholipids may differ greatly from the inner to the outer leaflet of the biomembrane layer [4,5]. Again, this is related to the differences in chemical... 

NMR measurements on deuterated phospholipid bilayers and phospho-lipid/eholesterol mixtures, measurements of self-diffusion of phosphatidyleho-lines in lipid bilayers, and finally pressure effeets on the strueture and phase behaviour of model biomembranes eonsisting of phospholipid bilayers with incorporated peptides will be discussed. 

Phosphatidylcholines are the most prominent components of biological membranes and therefore often serve as model biomembrane systems in biophysical studies.Due to their amphiphathic character, phospholipids have a strong tendency to spontaneously form bilayer structures when... 

Membrane permeability is another important parameter for drugs, because it is related to intestinal absorption and brain penetration. Lipophilicity is also useful in predicting these phenomena. In addition, liposome with phospholipid would be more reliable for measuring biomembrane permeability. Recently, some groups reported an EKC approach with phospholipid vesicles (56-58). 

IJ Cartwright. Separation and analysis of phospholipids by thin layer chromatography. In JM Graham, JA Higgins, eds. Methods in Molecular Biology. Vol. 19 Biomembrane Protocols I. Isolation and Analysis. Totowa, NJ Humana Press, 1993, pp 153-167. 

Hub HH, HupferB, Koch H, Ringsdorf H. Polyreactions in ordered systems. 20. Polymerizable phospholipid analogs—new stable biomembrane and cell models. Angew Chem Int Ed... 

Ishihara et al. [171,172] have been studying hemocompatible polymers with phospholipid polar groups. Their idea was to synthesize a polymer possessing a strong affinity for phospholipids from blood, which could be organized to form a biomembrane-like assemblage on the polymer surface. Phospholipid... 

The photoreduction of AuC14 in the presence of dimyristoyl-L-alpha-phosphati-dyl-DL-glycerol, which is a negatively charged phospholipid, gives rise to Au NPs coated through electrostatic adsorption of a biomolecule, leading to a nanosized model of a biomembrane [148]. 

In all three cases amphiphiles orient spontaneously to form structures resembling the phospholipid arrangement in biomembranes. These membrane models allow a variety of investigations of physical membrane properties which could not be conducted with the complex natural systems. 

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