Protein micellar mass

Burcon NutraScience Corporation, a venture capital company founded at the turn of the century and specialized in the commercialization of canola proteins, adopted a unique process based on salt extraction [47], Saline of 0.15 M was used as the extractant. As shown in Figure 4.9, after extraction the resulting protein solution was concentrated by ultrafiltration to a concentration in excess of 200 g/L, and then diluted with chilled water at a temperature below 15°C to form a protein micellar mass (PMM), which accounted for 40-60% extracted protein, depending on the initial protein concentration and dilution ratio. PMM was settled, separated from supernatant and dried to obtain a protein isolate with a protein content over 100% (N X 6.25). The supernatant was processed to recover additional proteins by further... 

Ferritin is another protein that is important in the metabolism of iron. Under normal conditions, it stores iron that can be called upon for use as conditions require. In conditions of excess iron (eg, hemochromatosis), body stores of iron are greatly increased and much more ferritin is present in the tissues, such as the liver and spleen. Ferritin contains approximately 23% iron, and apoferritin (the protein moiety free of iron) has a molecular mass of approximately 440 kDa. Ferritin is composed of 24 subunits of 18.5 kDa, which surround in a micellar form some 3000-4500 ferric atoms. Normally, there is a little ferritin in human plasma. However, in patients with excess iron, the amount of ferritin in plasma is markedly elevated. The amount of ferritin in plasma can be conveniently measured by a sensitive and specific radioimmunoassay and serves as an index of body iron stores. 

Rate of protein transfer to or from a reverse micellar phase and factors affecting the rate are important for the practical applications of RME for the extraction and purification of proteins/enzymes and for scale-up. The mechanism of protein exchange between two immiscible phases (Fig. 2) can be divided into three steps [36] the diffusion of protein from bulk aqueous solution to the interface, the formation of a protein-containing micelle at the interface, and the diffusion of a protein-containing micelle in to the organic phase. The reverse steps are applicable for back transfer with the coalescence of protein-filled RM with the interface to release the protein. The overall mass transfer rate during an extraction processes will depend on which of these steps is rate limiting. 

Dungan et al. [186] have measured the interfacial mass transfer coefficients for the transfer of proteins (a-chymotrypsin and cytochrome C) between a bulk aqueous phase and a reverse micellar phase using a stirred diffusion cell and showed that charge interactions play a dominant role in the interfacial forward transport kinetics. The flux of protein across the bulk interface separating an aqueous buffered solution and a reverse micellar phase was measured for the purpose. Kinetic parameters for the transfer of proteins to or from a reverse micellar solution were determined at a given salt concentration, pH, and stirring... 

FIGURE 8.7 Negative adsorption (steric exclusion) of a solute S from the surface of a protein molecule or particle, (a) Schematic explanation, (b) Relation between nonsolvent water vrns and molecular radius Rs of the solute (mostly sugars) for micellar caseinate a scale of molar mass (M, in Da) is also given. Rw is the radius of a water molecule. 

It should be noted that, generally, in the case of using the second method of solubilization—solution of the dry protein preparation in micellar solution—the contents of the comixtures, both proteins and low-molecular mass compounds (salts), could be controlled in the final solution. 

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In the first case, the total water volume which pre-existed in the empty micelle is maintained in the enzyme-containing micelle, and there is an enlargement of the size of the micelle (with the necessary reequilibration of the system to respect mass balance). In the second case, it is the original micellar size which is maintained. This latter model demands that water is expelled from the water pool when the protein comes in, this water being reequilibrated in the overall system. 

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