Proteins denaturization

The mechanism of antiperspinant action has not been fully estabHshed but probably is associated with blockage of ducts leading to the surface by protein denaturation by aluminum salts. The FDA has mandated that an antiperspinant product must reduce perspiration by at least 20% and has provided some guidelines for testing finished products. Some antiperspinant chemicals are Hsted in Table 14 (63). 

Product recoveiy from reversed micellar solutions can often be attained by simple back extrac tion, by contacting with an aqueous solution having salt concentration and pH that disfavors protein solu-bihzation, but this is not always a reliable method. Addition of cosolvents such as ethyl acetate or alcohols can lead to a disruption of the micelles and expulsion of the protein species, but this may also lead to protein denaturation. These additives must be removed by distillation, for example, to enable reconstitution of the micellar phase. Temperature increases can similarly lead to product release as a concentrated aqueous solution. Removal of the water from the reversed micelles by molecular sieves or sihca gel has also been found to cause a precipitation of the protein from the organic phase. 

Reversed-phase chromatography rehes on significantly stronger-hydrophobic interactions than in HIC, which can result in unfolding and exposure of the interior hydrophobic residues, i.e., leads to protein denaturation and irreversible inactivation as such, RPC depends... 

Ion exchange resins are also useful for demineralising biochemical preparations such as proteins. Removal of metal ions from protein solutions using polystyrene-based resins, however, may lead to protein denaturation. This difficulty may be avoided by using a weakly acidic cation exchanger such as Bio-Rex 70. 

FIGURE 3.4 The dependence of AG on temperatnre for the denaturation of chymotrypsinogen. (Adapted from Brandts, J. K, 1964. The thermodynamics of protein denaturation. I. The denaturation of e.hymotryjosinogeti. femrntA of the American Chemical Society m-.429I-430I.)... 

Figure 26.7 A representation of protein denaturation. A globular protein loses its specific three-dimensional shape and becomes randomly looped.

Hypothermia—Indirect cryodestruction Metabolic uncoupling Energy deprivation Ionic imbalance Disruption of acid-base balance Waste accumulation Membrane phase transitions Cytoskeletal disassembly Frozen State—Direct cryodestruction Water solidification Hyperosmolality Cell-volume disruption Protein denaturation Tissue shearing Intracellular-ice propagation Membrane disruption Microvascular Thawed State Direct effects... 

The presence of nanopartides suspended within the starch matrix would ensure continuous release of ions into the nutrient media. Copper ions released by the nanopartides may attach to the negatively charged bacterial cell wall and rupture it, thereby leading to protein denaturation and cell death [31]. The attachment of both ions and nanopartides to the cell wall caused accumulation of envelope protein precursors, which resulted in dissipation of... 

TCA is a chemical cauterant the application of which to the skin causes protein denaturation, so called keratocoagulation, resulting in a readily observed white frost. The degree of tissue penetration and ensuing injury by a TCA solution is dependent on several factors, including strength of TCA used, skin preparation and anatomic site. 

Surface films much more viscous than the bulk of the material occur also at a constant temperature. Thus, proteins denature at interfaces and produce interfacial films. Evaporation of the solvent into the atmosphere leaves a layer of higher concentration on the surface of the solution. As, usually, higher concentration means higher viscosity, a viscous surface film results. Again, the loss of solvent may be so great that the films solidify and a solid foam of an indefinite persistence is obtained. As a first approximation, the foam on milk consists of evaporated milk. 

Texturization is not measured directly but is inferred from the degree of denaturation or decrease of solubility of proteins. The quantities are determined by the difference in rates of moisture uptake between the native protein and the texturized protein (Kilara, 1984), or by a dyebinding assay (Bradford, 1976). Protein denaturation may be measured by determining changes in heat capacity, but it is more practical to measure the amount of insoluble fractions and differences in solubility after physical treatment (Kilara, 1984). The different rates of water absorption are presumed to relate to the degree of texturization as texturized proteins absorb water at different rates. The insolubility test for denaturation is therefore sometimes used as substitute for direct measurement of texturization. Protein solubility is affected by surface hydrophobicity, which is directly related to the extent of protein-protein interactions, an intrinsic property of the denatured state of the proteins (Damodaran, 1989 Vojdani, 1996). 

We also noticed that the molecular area decreases gradually when the surface pressure is held at a certain value. Two possible explanations for this are (1) there may be some leakage of protein molecules from the surface into the subphase, since the protein is water soluble (2) protein denaturation may be taking place at the air-water interface. 

In this activity, egg whites are used as an example of a protein. Denaturing will be accomplished by lowering the pH and by increasing the temperature. 

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