Proteins phase separation exhibited

Access to Energies That Sustain Life Derives from a Special Phase Separation Exhibited by Proteins... 

Conformational and phase transitions can potentially be indicative of the primary structure of thermosensitive macromolecules. Indeed, depending on the relative location of H- and P-blocks, as well as on the variation of their length, the chains can either undergo conformational transition accompanied by phase separation, or they can exhibit only the conformational changes without macroscopic phase transitions, i.e. the behaviour observed in the case of protein-like HP-copolymers. Therefore, the solution behaviour of separated fractions of these NVCl/NVIAz-copolymers in an aqueous medium at different temperatures is very important. 

Although some membrane proteins are known to interact with cholesterol, cholesterol interactions with other lipids have been studied much more thoroughly. Most notably, cholesterol interacts strongly with sphingomyelin, perhaps by forming complexes, which results in a liquid-liquid phase separation of cholesterol-rich and cholesterol-poor phases (13). The cholesterol-rich phases exhibit more chain order and therefore are referred to as liquid-ordered (lo) phases, whereas the cholesterol-poor phases are called liquid-disordered (Id) phases. 

Protein-water solutions sometimes exhibit critical solution temperatures (see Chapter 5 for a discussion of phase separation). Phase transitions are important not only in manufacture and formulation, but also because they... 

Before starting a preparative chiral separation it is essential to identify a chiral stationary phase (CSP) exhibiting good chiral recognition ability. This is usually done with an analytical column because it is less substance- and time-consuming. A stationary phase mostly composed of silica gel with only a few chiral elements will be rapidly overloaded. In this event, even if the phase exhibits useful properties for analytical purposes, it will not be appropriate for preparative applications this is the case for protein-based phases [102, 103], Most chiral stationary phases have relatively low saturation capacity, so the enantiomer separations are usually done under strongly nonlinear conditions [103], Accordingly, the accurate determination of the adsorption isotherms of the two enantiomers on a CSP is of fundamental importance to allow computer-assisted optimization to scale up the process. 

The solid phase of bread crumb can be viewed as a composite material where amylose, amylopectin and protein form separated phases due to poor thermodynamic miscibility of the different polymers. Composites are characterized by exhibiting mechanical properties that cannot be achieved with the individual constituents alone, but are dependent on the interface between the components. A sharp interface as found between starch and protein provides strong evidence of little polymer interdiffusion and weak interfacial adhesion.14 The present results suggest that starch forms a continuous phase in bread which has also been confirmed with confocal scanning laser microscopy.15 The presence of a protein phase reduces the continuity of the starch phase and, thus, reduces the cohesion of the material as revealed by a comparison of the breaking stresses of aged flour and starch gels (data not shown).16... 

The hydrophobic polyurethane block copolymer was chosen because phase-separated samples had been shown by an in vitro assay to exhibit a greater platelet adhesion from human blood than samples having a mixed, nonphase-separated structure (7). The hydrophobic styrene-butadiene-styrene (SBS) block copolymer was chosen because of the ease with which the morphology could be controlled (8). The block copolymer having hydrophilic blocks of poly(ethylene oxide) and hydrophobic polystyrene blocks (PS-PEO) was chosen to examine the effect of the more hydrophilic blocks on the protein interaction. 

Stepwise increases in oil-like character, as when the mildly oil-like Val (V) residue is replaced by the very oil-like Phe (F) residue, cause the add-base titration curves to be shifted to higher pH values and to be steeper. The energy required to drive the model protein from the phase separated, contracted state to the swollen, relaxed state is proportional to the width of the curve, that is, inversely proportional to the steepness of the curve. Accordingly, the model protein with the steepest curve exhibits the most efficient function for performing the work of lifting a weight. 

As demonstrated in Figure 5.3 for several model proteins, essentially unlimited solubility occurs at low temperature, and phase separation (insolubility) occurs as the temperature is raised. Also, for our model protein composi-tions, - the curvature of the coexistence line is inverted, having the shape of a valley instead of a smooth mountain peak. Because of this we call the phase transition, exhibited by elastic-contractile model proteins, an inverse temperature transition. Even more compelling reasons exist for the inverse temperature transition label. 

By T,-type, we mean polymers that exhibit inverse temperature transitions in which the protein-based polymers hydrophobically associate on raising the temperature. T, represents the onset temperature for the transition. For the elastic-contractile model proteins of interest here, the inverse temperature transition is seen as a phase separation resulting from both intermolecular and intramolecular hydrophobic association. On raising the temperature... 

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