Denaturants/denaturation

Protein-Based Adhesives. Proteia-based adhesives are aormaHy used as stmctural adhesives they are all polyamino acids that are derived from blood, fish skin, caseia [9000-71 -9] soybeans, or animal hides, bones, and connective tissue (coUagen). Setting or cross-linking methods typically used are iasolubilization by means of hydrated lime and denaturation. Denaturation methods require energy which can come from heat, pressure, or radiation, as well as chemical denaturants such as carbon disulfide [75-15-0] or thiourea [62-56-6]. Complexiag salts such as those based upon cobalt, copper, or chromium have also been used. Formaldehyde and formaldehyde donors such as h exam ethyl en etetra am in e can be used to form cross-links. Removal of water from a proteia will also often denature the material. 

Denaturierung, /. denaturing, denaturation. Denaturierungsmittel, n. denaturant. denaturisieren, v.t. = denaturieren. Dendrachst, Dendritenachst m. dendritic agate. 

Because the tertiary structure of a globular protein is delicately held together by weak intramolecular attractions, a modest change in temperature or pH is often enough to disrupt that structure and cause the protein to become denatured. Denaturation occurs under such mild conditions that the primary structure remains intact but the tertiary structure unfolds from a specific globular shape to a randomly looped chain (Figure 26.7). 

An efficient cooling system minimizes protein denaturation (denaturation would otherwise occur due to the considerable amount of heat generated during the homogenization process). Ho-mogenizers capable of handling large quantities of cellular suspensions are now available, many of which can efficiently process several thousand litres per hour. 

Although RP-HPLC has proven its analytical usefulness, its routine application to analysis of specific protein preparations should be undertaken only after extensive validation studies. HPLC in general can have a denaturing influence on many proteins (especially larger, complex proteins). Reverse-phase systems can be particularly harsh, as interaction with the highly hydrophobic stationary phase can induce irreversible protein denaturation. Denaturation would result in the generation of artifactual peaks on the chromatogram. 

A plot of the logarithm of the rate constant for unfolding, ka, against the concentration of denaturant is found to be close to linear for many proteins at [denaturant] > [denaturant] 50% ... 

For 02 and some other small proteins, but not in general, the folding rate constant, kf, follows a similar relationship for [denaturant] < [denaturant] 50% ... 

One of the major problems that a biochemical engineer will encounter is that of the stability of protein materials. The biological function of the molecule is determined by its secondary and tertiary structures and if these are upset irreversibly then the protein becomes denatured. Denaturation can occur under relatively mild conditions as proteins are usually stable over only very narrow ranges of pH (e.g. 5-8) and of temperature (e.g. 10-40°C). The boiling of an egg illustrates this point. In its uncooked form the white is a slimy clear protein solution, but under acidic conditions, or when put in boiling water, the solution gels to white solid. 

Although less frequently discussed, heat processes often influence the textures and chemistries of the intermediate and end products, and thermal treatments are not without consequences on milk proteins that are denatured. Denaturation of proteins occurs under precise conditions of pH, temperature and ionic strength leading to their unfolding. Denaturation is significantly slower when proteins are near their isoelectric point. Only (3-lactoglobulin is irreversibly denatured at pH 7 and 70°C a-lactalbumin is denatured at pH 6.7 and 65°C. Aggregation of these proteins, besides hydrophobic... 

The first reaction to be discussed is denaturation. Denaturation is involved in most structure forming processes although gels may form from already denatured proteins. It is important to control the denaturation process in order to obtain structures with the desired textural properties. Unfortunately most studies on protein denaturation have been made by biochemists mainly interested in the native structure. One definition given... 

Protein digestion begins in the stomach, where the acidic environment favors protein denaturation. Denatured proteins are more accessible as substrates for proteolysis than are native proteins. The primary proteolytic enzyme of the stomach is pepsin, a nonspecific protease that, remarkably, is maximally active at pH 2. Thus, pepsin can be active in the highly acidic environment of the stomach, even though other proteins undergo denaturation there. 

What happens when the three-dimensional structure of a protein is disrupted Think of the difference between the consistency of a raw egg white and that of a hard-boiled egg. When the forces holding a polypeptide chain in its three-dimensional shape are broken, the protein is unfolded in a process called denaturation. High temperatures can denature proteins, which is why cooking foods that contain proteins results in the proteins denaturation. Denatured proteins form the solid white of a hard-boiled egg. In addition, proteins can be denatured by extremes in pH, mechanical agitation, and chemical treatments. When egg whites are beaten, the proteins are denatured, as shown in Figure 19.4. Because the folded shape of a protein is essential for its function, denaturation of a protein results in loss of its function. This is one reason why organisms can live only in a narrow temperature and pH range. 

Ethyl Alcohol, Denatured, Denatured alcohol. Ethyl alcohol to which has been added some substance or substances which, while allowing the use of the alcohol in... 

First, almost aU enzymes become denatured if they are heated much above physiological temperatures and the conformation of the enzyme is altered, often irreversibly, with loss of catalytic activity. Exceptions are the thermophylic microorganisms, which are capable of working within a much broader range of temperature. The loss of catalytic activity if often due to denaturation denaturation is chemically a very complex process, considering a large molecular size of proteins and the complexity of their three-dimensional stracture. 

The adsorption of large polar molecules is expected to produce large unfolding of the protein, possibly terminating with its denaturation. Denaturation can be considered as a phase transition, characterized by a jump discontinuity of the adsorption isotherm, between native-like state (with bulk fractal dimension D = 3 and surface fractal dimension D = 2.1 - 2.2) and the denatured state (in which the protein can be seen as an excluded-volume polymer with D =5/3 [57]). Denaturation is therefore associated with a sudden variation of the fractal dimension of the protein. 

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