Thermodynamic lead-protein interactions

We have seen earlier in this chapter how the self-assembly of casein systems is sensitively affected by temperature. Another thermodynamic variable that can affect protein-protein interactions in aqueous media is the hydrostatic pressure. Static high-pressure treatment causes the disintegration of casein micelles due to the dismption of internal hydro-phobic interactions and the dissociation of colloidal calcium phosphate. This phenomenon has been used to modify the gelation ability of casein without acidification as a consequence of exposure of hydrophobic parts of the casein molecules into the aqueous medium from the interior of the native casein micelles (Dickinson, 2006). High-pressure treatment leads to a reduction in the casein concentration required for gelation under neutral conditions, especially in the presence of cosolutes such as sucrose (Abbasi and Dickinson, 2001, 2002, 2004 Keenan et al., 2001). 

On the basis of available data, it would appear that there are several possible reasons that may account for the observed decrease in surface activity of proteins, depending on the strengths of their thermodynamically favourable interactions with different polysaccharides. In the case of a rather weak interaction, which does not lead to the formation of a stable complex between protein and polysaccharide, the decrease in the surface activity of protein is evidently determined by the corresponding... 

It seems that there is probably greater availability of positively charged residues on the adsorbed protein for electrostatic interaction with sulfate groups of the anionic polysaccharide. This could lead to a greater extent of neutralization of dextran sulfate as a result of complex formation, and consequently to a lower thermodynamic affinity of the complexes for the aqueous medium and a lower value of the ( -potential for emulsion droplets in bilayer emulsions. 

The simple ternary complex model (Fig. 2A) describes the binding of ligands to GPCRs, leading to the activation of G protein (De Lean et ah, 1980 Lefkowitz et at, 1993). This model is based on the four equilibrium reactions that account for all of the thermodynamically possible interactions between the three species ligand, GPCR, and G protein. 

Before discussing the role of proteins in cold acclimation the physical effects caused by low temperature are briefly considered. A decrease of temperature leads to altered rates of enzymatic catalysis. Formation of hydrogen bonds and electrostatic interactions are thermodynamically more stable at a lower temperature whereas hydrophobic interactions are... 

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