Phase boundary protein

Kaltashov I.A., Eyles S.J. Crossing the phase boundary to study protein dynamics and function combination of amide hydrogen exchange in solution and ion fragmentation in the gas phase. J. Mass Spectrom. 2002, 37, 557-565. 

The potential differences, /, at different phase boundaries, as mentioned before, have been found to have many industrial applications. The application of electrophoresis to the separation and purification of proteins has also been discussed. Both electrophoresis and electroosmosis have attained a certain amount of industrial application. 

In order to obtain a thermodynamically stable micro emulsion, the analysis of the phase behaviour is indispensable. With bovine serum albumin instead of an enzyme (because of the cost of the bio-catalyst) phase behaviour studies are shown in Fig. 2. A strong shift of the phase boundary is observed, yielding a system that solubilises much less water in the presence of the protein. In case of hydrophobic enzymes, the addition of dry lyophilised protein to an already prepared reverse micellar solution can also work well [53]. 

Skim milk can be considered as a two-phase system consisting of casein-colloidal calcium phosphate micelles in quasi-equilibrium with an aqueous solution of salts and proteins the phase boundary is ill-defined because of the intimate association between the calcium phosphate and the caseins (phosphoproteins). 

In conclusion thermal degradation studies on Nautilus pompilius indicate that mineralizing matrix and aragonite shell represent a true structural entity. By the sharing of oxygens in protein and mineral lattices we will generate phase boundaries of the type that are present, for instance, in the common clay mineral kaolinite. Here, aluminum octahedra and silica tetrahedra incorporate the same oxygens and hydroxyls, and layers composed of octahedra and tetrahedra arise (Fig. 13). 

Studies of membrane-associated effects of a series of drugs on PLA2 have been undertaken to investigate the possibility that some proteins and drugs interact with the bilayer at phase boundaries or with defect structures necessary for PLA2 activity. The direct or indirect effect of drugs on such boundaries or defects could then affect membrane-protein interactions. 

Electric double layers at phase boundaries pervade the entire realm of Interface and colloid science. Especially in aqueous systems, double layers tend to form spontaneously. Hence, special precautions have to be taken to ensure the absence of charges on the surfaces of particles. Insight into the properties of double layers is mandatory, in describing for Instance electrosorption, ion exchange, electrokinetics (chapter 4), charged monolayers (Volume III), colloid stability, polyelectrolytes and proteins, and micelle formation of ionic surfactants, topics that are intended to be treated in later Volumes. The present chapter is meant to Introduce the basic features. 

Mattison, K.W. Brittain, I.J. Dubin, P.L. Protein-polyelectrolyte phase boundaries. Biotechnol. Progr. 1995, 11 (6), 632-637. 

Before a protein molecule can adsorb and exert its influence at a phase boundary or take part in an interfacial reaction, it must arrive at the interface by a diffusion process. If we assume there is no barrier to adsorption other than diffusion, simple diffusion theory may be applied to predict the rate of adsorption. Under these conditions, after formation of a clean interface, all the molecules in the immediate vicinity will be rapidly adsorbed. The protein concentration in a sublayer, adjacent to the interface.and of several molecular diameters in thickness, will thus be depleted to zero. A diffusion process then proceeds from the bulk solution to the sublayer. The rate of adsorption, dn/dt, will be simply equal to the rate of this diffusion step given by classical diffusion theory (Crank, 1956) as... 

Phase boundaries were also developed for p-lactoglobulin, chicken egg albumin, lysozyme, ribonuclease, and trypsin, all at r=100, a weight ratio at which polymer saturation appears to take place (see Discussion section). For each protein, pHcritical was converted to net negative surface charge (Zpr) per unit protein surface area (A), using potentiometric titration curves (26-31) and hydrodynamic radii (32) found in literature. Plots of surface charge density (Zpr/A) vs. I are shown in Figure 3. 

Figure 3. Phase boundaries (r = 100) of six proteins, plotted as net surface charge density (net charge/nm ) vs. 1 (ionic strength) (O) bovine serum albumin ( ) lysozyme (A) ribonuclease (A) chicken egg albumin ( ) -lactoglobulin and ( ) trypsin.

Analyses of phase boundaries reveal evidence for polymer saturation in the presence of excess protein. Phase boundaries also facilitate comparisions of the behavior of various proteins. The failure of net surface charge density as a universal parameter for protein-polyelectrolyte interaction is believed to be related to the existence of "charge patches" on the protein surface. The determination of a more realistic protein charge parameter possesses great importance, since the ionic interactions of proteins are exploited in a variety of applications, including protein purification via ion exchange liquid chromatography. 

Detergents solubilize water insoluble substances. They merge into the inter-boundary layers of naturally occurring proteins at various phase boundaries, thus influencing mass-transport processes in natural systems. Hence the toxic effects of detergents to aquatic organisms are closely related to their interactions with lipids and proteins in biological membranes. 

Lipids do not form an ideal fluid, but exist as a mixture of diverse species that show preferences in associating with each other as a result of head group attractions or repulsions, and packing effects in the hydrocarbon core. Small transient microdomains are formed by specific and nonspecific protein—protein, protein-lipid, and lipid-lipid interactions. A variety of techniques have shown that membrane proteins are surrounded by a dynamic boundary layer of lipids with an average composition distinct from the bulk phase. Membrane proteins, through their preferential association with specific lipids, can induce microdomains consisting of these boundary lipids and the lipids that interact preferentially with the boundary lipids. In turn, these microdomains enhance the formation of protein clusters. 

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