Surface extrinsic

Proteins either strengthen the membrane structure (building proteins) or fulfil various transport or catalytic functions (functional proteins). They are often only electrostatically bound to the membrane surface (extrinsic proteins) or are covalently bound to the lipoprotein complexes (intrinsic or integral proteins). They are usually present in the form of an or-helix or random coil. Some integral proteins penetrate through the membrane (see Section 6.4.2). 

Fig. 3 Structural model of the cell membrane. The membrane is composed of a bimolecular leaflet of phospholipid with the polar head groups facing the extracellular and cytosolic compartments and the acyl groups in the middle of the bilayer. Integral membrane proteins are embedded in the lipid bilayer. Integral proteins are glycosylated on the exterior surface and may be phosphorylated on the cytoplasmic surface. Extrinsic membrane proteins, peripheral proteins, are linked to the cytosolic surface of the intrinsic proteins by electrostatic interactions. (From Ref. l)...

Among surface states, there are some that originate simply from the sudden discontinuity in the ciystal lattice these are intrinsic surface states. They are sorted, depending on their source, into two categories Tamm states, which are caused by lattice deformation, and Schockley states, caused by the unsaturated bonds on the surface. There also appears on the real surfaces extrinsic surface states due to the presence of foreign species on the surface of the solid, namely adsorbed atoms or molecules originating from a gaseous phase. 

Deconstructing the Supra-Molecular Interactions at Surfaces - Extrinsic Synthons... 

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. 

Surface states can be divided into those that are intrinsic to a well ordered crystal surface with two-dimensional periodicity, and those that are extrinsic [25]. Intrinsic states include those that are associated with relaxation and reconstruction. Note, however, that even in a bulk-tenuinated surface, the outemiost atoms are in a different electronic enviromuent than the substrate atoms, which can also lead to intrinsic surface states. Extrinsic surface states are associated with imperfections in the perfect order of the surface region. Extrinsic states can also be fomied by an adsorbate, as discussed below. 

Factor VII. This is a vitamin K-dependent serine protease that functions in the extrinsic coagulation pathway and catalyzes the activation of Factors IX and X. Factor VII is present constitutively in the surface membrane of pericytes and fibroblasts in the adventitia of blood vessels, vascular endothehum, and monocytes. It is a single-chain glycoprotein of approximately 50,000 daltons. 

Wear. Ceramics generally exhibit excellent wear properties. Wear is deterrnined by a ceramic s friction and adhesion behavior, and occurs by two mechanisms adhesive wear and abrasive wear (43). Adhesive wear occurs when interfacial adhesion produces a localized Kj when the body on one side of the interface is moved relative to the other. If the strength of either of the materials is lower than the interfacial shear strength, fracture occurs. Lubricants (see Lubricants and lubrication) minimize adhesion between adj acent surfaces by providing an interlayer that shears easily. Abrasive wear occurs when one material is softer than the other. Particles originating in the harder material are introduced into the interface between the two materials and plow into and remove material from the softer material (52). Hard particles from extrinsic sources can also cause abrasive wear, and wear may occur in both of the materials depending on the hardness of the particle. 

Singer and Nicolson also pointed out that proteins can be associated with the surface of this bilayer or embedded in the bilayer to varying degrees (Figure 9.6). They defined two classes of membrane proteins. The first, called peripheral proteins (or extrinsic proteins), includes those that do not penetrate the bilayer to any significant degree and are associated with the membrane by virtue... 

The conformation of bovine myelin basic protein (MBP) in AOT/isooctane/water reversed micellar systems was studied by Waks et al. 67). This MBP is an extrinsic water soluble protein which attains an extended conformation in aqueous solution 68 but is more density packed at the membrane surface. The solubilization of MBP in the AOT reversed micelles depends on the water/AOT-ratio w0 68). The maximum of solubilization was observed at a w0-value as low as 5.56. The same value was obtained for another major protein component of myelin, the Folch-Pi proteolipid 69). According to fluorescence emission spectra of MBP, accessibility of the single tryptophane residue seems to be decreased in AOT reversed micelles. From CD-spectra one can conclude that there is a higher conformational rigidity in reversed micelles and a more ordered aqueous environment. 

FXa complexes bind to and neutralize tissue factor/ FVIIa complexes, the key starting point of the extrinsic clotting cascade (see earlier) (Fig. 7). Heparin is able to enhance this reaction by direct binding to the complex and by releasing TFPI from the unaltered vessel wall, which then can access the TF-exposing surface. 

Two main apoptotic pathways have been identified in mammalian cells the extrinsic pathway that is activated by the binding of ligands to cell-surface death receptors, and the intrinsic pathway that involves the mitochondrial release of cytochrome cP The activation of extrinsic and intrinsic apoptotic pathways promotes the cleavage into the active form of the pro-caspase-8 and pro-caspase-9, respectively, that mainly determine the activation of effector caspase-3. ° The intrinsic pathway is the main apoptotic pathway activated by chemotherapeutic drugs, while the cytotoxic drug-induced activation of the extrinsic pathway is a more controversial issue. ... 

Initiation of the fibrin clot in response to tissue injury is carried out by the extrinsic pathway. How the intrinsic pathway is activated in vivo is unclear, but it involves a negatively charged surface. The intrinsic and extrinsic pathways converge in a final common path-vray involving the activation of prothrombin to thrombin and the thrombin-catalyzed cleavage of fibrinogen to form the fibrin clot. The intrinsic, extrinsic, and final common pathways are complex and involve many different proteins (Figure 51-1 and Table 51-1). In... 

Frequently, adsorption proceeds via a mobile precursor, in which the adsorbate diffuses over the surface in a physisorbed state before finding a free site. In such cases the rate of adsorption and the sticking coefficient are constant until a relatively high coverage is reached, after which the sticking probability declines rapidly. If the precursor resides only on empty surface sites it is called an intrinsic precursor, while if it exits on already occupied sites it is called extrinsic. Here we simply note such effects, without further discussion. 

The shape of an object is a descriptor of the outline of its external surface only. Thus the shape of an object is a property that reflects the recognized pattern of relationships among all the points that constitute its external surface. The difference between the shapes of two objects arises from the differences between the patterns of relationships among these point coordinates corresponding to the two shapes. While the size of an object, for example a material particle, is an indicator of the quantity of matter contained in it, its shape is concerned with the pattern according to which this quantity of matter is assembled together. Shape is an intrinsic rather than an extrinsic characteristic in that it is not additive. 

The fluidity of blood is a result of the inhibition of a complex series of enzymic reactions in the coagulation cascade (see Fig. 10). When triggered either intrinsically (by contact with foreign surfaces ), or extrinsically (by tissue factors from damaged cells), inactive proenzymes (factors XII, XI, IX, and X) are transformed into activated pro-teinases (XHa, XIa, IXa, and Xa, respectively). Each proteinase catalyzes the activation of the following proenzyme in the sequence, up to formation of thrombin (Factor Ha), another proteinase that catalyzes partial... 

Proteins are also associated with the lipid bilayer and essentially float within it. Intrinsic proteins are embedded within and span the membrane, and extrinsic proteins are found on the internal or external surface of the... 

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