Surface coagulation, protein

Antibodies directed against (32 -GPI further enrich the protein on the cell surface but these promote a p38 Map-kinase signalling cascade which results in increased expression of tissue factor (TF) and reduced expression of thrombomodulin on the surface of cells. TF is a major initiator of coagulation and increased levels of TF expression have been measured on endothelial cells treated with anti-phospholipid antibodies and on monocytes both ex vivo and in vivo (Yasuda et al., 2005 Lopez-lira et al., 2005, Lopez-Pedrera et al., 2006). Thrombomodulin is a potent anti-coagulant protein which limits activation of thrombin, so the net result of circulating anti-phospholipid antibodies is to usurp the anti-coagulative, protective mechanism and initiate a pro-coagulation cascade. 

The appearance of anionic phospholipids, particularly phosphatidylserine, on the cell surface activates prothrombinase complex culminating in the formation of thrombin (Bevers et al., 1982 Connor et al., 1989). The assay can be performed with pure coagulation proteins and specific chromogenic substrates to produce a very sensitive test to detect the appearance of phosphatidylserine on cell surfaces. Nevertheless, it has been shown that changes in the disposition of phosphatidylethanolamine and sphingomyelin may interfere with the ability of phosphatidylserine-containing membranes to activate prothrombinase (Smeets et al., 1996). 

F. 45.6. Anti-thrombotic effects of thrombin. Thrombin, bound to thrombomodulin on the endothehal cell surface, activates protein C. Activated protein C, in complex with protein S, binds to the platelet membrane, and the activated complex destroys Factors Va and Villa, thereby inhibiting the coagulation cascade. 

Surface Coagulation. During the preparation of solutions of certain proteins, it is observed that an insoluble precipitate may form. This occurs as a result of interfacial action and is accentuated by excessive shaking. The mechanism appears to be roughly as follows. As fresh interface is formed, protein molecules adsorb and unfold to an extended chain conformation. At a given surface density, the solubility limit of the protein at the surface is reached and precipitation occurs. This is a special case of precipitation since it involves a transition from a two-dimensional (monolayer) to a three-dimensional state (coagulated protein). The solubility limit is usually characterized by a... 

The work discussed here has shown that suspensions of platelets and red cells in a physiological medium can provide information for platelet surface interactions. Evidence is provided on the dynamic features of platelet-surface adhesion and detachment which indicates that more than one sequence of adhesion, detachment and re-adhesion can lead to the same net platelet adhesion. Surface generated substances, such as A DP and serotonin from platelets and thrombin from the coagulation pathway, may strongly influence the function of platelets approaching a surface. The supply of these substances depends on the presence of flow and continued arrival of platelets at a surface. The reactivity of surface-bound protein may be altered by platelet adhesion and detachment. This may occur as a result of deposition of cell membrane components, replacement of the original substrate with protein secreted from platelets or possibly by enzymatic digestion of surface bound protein. 

Similar interactions were observed between the coagulant protein and the anionic surfactant sodium bis(2-ethyl-l-hexyl)sulfosuccinate (AOT) when monitored by surface tension probe [16]. 

In this work, the effects of the presence of anionic surfactants SDS and SDBS on the viscosity properties of the coagulant protein from Moringa oleifera are reported. The results of solution properties of the protein in the presence of SDS are verified by surface tension, circular dichroism, and fluorescence measurements reported earlier [15-18]. 

The intrinsic viscosity [t]] of the coagulant protein was measured for protein concentration, c, in the range 0.02—0.15 g/mL in 0.1 M NaCl. Solution environment such as presence of surfactants can affect protein conformation. To study interactions SDS and SDBS with the cor ulant protein, capillary viscosities of the surfactant/protein solutions were measured using a capillary viscometer. The protein concentration (% w/v) was kept constant at 0.05% whereas the surfactant concentration was varied up to concentrations higher than the critical micelle concentration (CMC). The protein solution was used as the reference standard for surfactant dissolved in 0.05% protein. The SDS (99% purity) was supplied by Sigma-Aldrich whereas SDBS was supplied by Fluka, and both surfactants were used without further purification. The measurements of surface tension, fluorescence, and circular dichroism spectral correlation coefficients of SDS solutions in the presence of protein were done in similar manner, and the details are described elsewhere [15-18]. 

In this section, the viscosity data was directly compared to earlier reported surface tension [15, 16], fluorescence [17], and CD [18] data of the coagulant protein-SDS interaction studies (Figure 3). Similar SDS concentration ranges were used, and it was convenient to divide the profiles into four different regions depending on the SDS concentration. 

R. Maikokera and H. M. Kwaambwa, Interfacial properties and fluorescenc e of a coagulating protein extracted from Moringa oleifera seeds and its interaction with sodium dodecyl sulphate, Colloids and Surfaces B, vol. 55, no. 2, pp. 173-178, 2007. 

H. M. Kwaambwa and R. Maikokera, Air-water interface interacaiion of anionic, cationic, and non-ionic surfactants with a coagulant protein extracaied from Moringa oleifera seeds studied using surface tension probe, Water SA, vol. 33,... 

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