Membranes intrinsic

The 20% soy lecithin (Table 7.17) and the 2% DOPC (Table 7.15) intrinsic permeabilities may be compared in a Collander equation, as shown in Fig. 7.44. The slope of the regression line, soy versus DOPC, is greater than unity. This indicates that the soy membrane is more lipophilic than the DOPC membrane. Intrinsic permeabilities are generally higher in the soy system. Three molecules were significant outliers in the regression metoprolol, quinine, and piroxicam. Metoprolol and quinine are less permeable in the DOPC system than expected, based on their apparent relative lipophilicities and in vivo absorptions [593]. In contrast, piroxicam is more permeable in DOPC than expected based on its relative lipophilicity. With these outliers removed from the regression calculation, the statistics were impressive at r2 0.97. 

Intact biological membranes are far more complex systems than even the lipid extracts (see Fig. 6). In hardly any case do the lipid components exceed 50% of the dry weight, as membranes intrinsically contain numerous proteins and various glycoconjugates. This diversity is most pronounced in the plasma membrane (irrespective of the genera) which is effectively amalgamated with the non-lipidic... 

Genetic analyses show that also the Chi a-binding proteins of red algae must be considered members of the LHC superfamily, even though they bind only Chi a and are associated only with PS I. [24] This shows that PBS (associated primarily with PS II) and membrane-intrinsic antennas of the LHC superfamily could coexist in the same chloroplast, and strongly supports a common evolutionary origin for all chloroplasts. [25]... 

In particular, the analysis of the contribution to k (oj) or a(to) due to the structural H20 may require explicit modeling of the membrane intrinsic field, for systems which contain biological membranes, and an altered ic (io) may obtain for such a case. Although the theory for the static complex permittivity, Kq in Eq. 

The V-type (or vacuolar-type) H+-ATPase was first found in fungal vacuoles and plant tonoplasts,13 l4) and is now known to be widely distributed in mammalian endomembrane systems.15) Like F-type ATPase, the subunit structure of the V-type ATPase is complicated. The membrane extrinsic sector is composed of 73 kDa, 58 kDa, 38 kDa, and 34 kDa subunits, while the membrane intrinsic sector is composed of 40 kDa 20 kDa and 16 kDa subunits. 

Bishop, R.E. Structural biology of membrane-intrinsic beta-barrel enzymes sentinels of the bacterial outer membrane. Biochim Biophys Acta 1778 (2008) 1881-1896. 

CORR applies equally to mitochondria and chloroplasts, and accounts for the fact that both of these organelles possess membrane-intrinsic electron transport systems along with discrete, extranuclear genetic systems. CORR rests on ten assumptions, or principles, as follows ... 

Most of the targets of plant defensive compounds are proteins and indeed many plant defensive agents are also proteins. Accordingly it is useful to briefly outline the various types of proteins encountered. Most proteins are water soluble but some function associated with membranes. The membrane-bound proteins can be firmly embedded in the phospholipid bilayer of the membrane (intrinsic or integral proteins) or are less intimately associated (extrinsic or peripheral membrane proteins). As outlined above, proteins may be monomeric, multisubunit or associated with large multisubunit complexes. 

Vorherr, T., Wrzosek, A., Chiesi, M., and Carafoli, E. (1993). Prot. Sci. 2, 339-347. Total synthesis and functional properties of the membrane-intrinsic protein phospholamban. 

FMN) and eight Fe-S clusters, all of which are located in a membrane-extrinsic arm of the L-shaped molecule that projects out into the matrix for reaction with NADH. This can be resolved from the membrane-intrinsic domain to give a soluble fraction known as IX (MW 360 kDa) that is active in NADH oxidation. Hirst and co-workers have shown that the membrane-extrinsic subcomplex obtained from beef heart mitochondria is highly electroactive when adsorbed on a PGE electrode.Figure 4-9 shows the voltammetry of a film of IA adsorbed on a rotating PGE disc electrode catalysing the interconversion of NAD and NADH which are each present in the cell solution at 1 mM concentration. 

Membrane- Intrinsic Extent of Oral Plasma Protein... 

This phenomenon is denoted feed-side concentration polarization and, in practice, affects mainly the fluxes of compounds of high sorption coefficient, even under turbulent hydrodynamic conditions over the membrane, as their permeability (and hence flux across the membrane) is high. It should at this point be emphasized that contrary to the non-ideal transport phenomena discussed earlier, feed-side concentration polarization is not a membrane-intrinsic phenomenon, but stems from poor design of the upstream flow conditions in practice it may in fact not be overcome owing to module design limitations (Baker et ah, 1997). 

Membrane permeability depends on the ability of the compound to diffuse through the unstirred layer and the membrane. Intrinsic permeability is linked to membrane partitioning as described below ... 

Fig. 10 Catalytic voltammetry of a film of nitrate reductase (a) cartoon showing the membrane-extrinsic sub-complex NarGH bound to the membrane-intrinsic Narl (left), and adsorbed instead on an electrode (right) (b) catalytic voltammetry of a film of NarGH adsorbed on a PGE electrode in the presence of different concentrations of nitrate (voltammo-gram without substrate is also shown). Note (arrowed) that the catalytic current for the experiment at low nitrate concentration passes through a maximum. (L. J. Anderson, D.). Richardson, J. N. Butt, Biochemistry 200, 40,11 294-11 307, with permission of the American Chemical Society.)...

The polymer solution is brought into contact with the glycerol. During thi.s time no phase separation occurs but due to the outdiffusion of NMP the polymer concentration at the topside of the solution increases. The second coagulation bath contains water and the demixing occurs immediately. In this way a thin dense toplayer is obtained supported by a porous sublayer. Table III. 11 summarizes some results of integrally skinned membranes prepared from different polymers with both the wet-dry and wet phase separation techniques. All membranes intrinsic selectivities indicating that no defects are present. 

There seems to be a historical reason for the difference in these two approaches. The solution-diffusion approach was established for the permeation of liquid and gas through the membrane before reverse osmosis membranes of practical usefulness were developed by the phase-inversion technique. Dense membranes without asymmetricity were prepared from polymeric materials, and their transport properties were measured, assuming that the membranes were defect-free and the transport parameters so produced were the values intrinsic to the material. The membrane with the highest separation capacity for a given polymer was believed to be that which could exhibit the transport properties intrinsic to the polymer. The goal of membrane production engineering was to ensure the membrane intrinsic transport properties of the polymeric material. This approach is still popular in the membrane manufacturing industry. 

Cq is the membrane intrinsic curvature, that is, the curvature of the membrane with zero deformation (e.g., a single layer of cylindrical molecules should have an intrinsic curvature of zero, but cone-shaped molecules will pack two dimensionally to have a curvature with no energy cost, k is the bending modulus, and is known as the saddle-splay modulus. As we can see in Figure 3.10, it is quite possible to have a curved membrane with a mean curvature of zero in the case of saddle-like deformations. Therefore, it becomes clear that to describe the energy cost of a saddle deformation the extra terms are necessary. 

Two distinct classes of proteins are synthesized by membrane-bound polysomes in cells which have a well-defined rough endoplasmic reticulum. They are secreted proteins which are destined for export or for transport to other cellular organelles, and membrane intrinsic proteins which have to be inserted asymetrically toward the noncytoplasmic face of the membrane. The role of the RER for the synthesis of secretory proteins is well established (Palade, 1975). For these proteins, compartmentalization regulates the different processes. They must be transferred across the hydrophobic bilayers... 

The basic structure of membranes is usually envisaged as the fluid-mosaic model of Singer and Nicholson. In this, amphiphilic lipids are arranged in a bimolecular layer with the hydrophobic moieties in the centre of the membrane and the hydrophilic head-groups at the two surfaces. Stability is achieved by various ionic or hydrophobic interactions between the lipids and the membrane proteins. The latter can be embedded within the membrane (intrinsic proteins) or attached to the surface (extrinsic proteins). Many membrane proteins are large enough to actually span the membrane. 

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