Denaturation of other biologically active proteins

Generally food processing causes irreversible denaturation followed by reactions of the thermally denatured proteins with other components that may lead to loss in food quality. However, in foods denaturation may have beneficial or detrimental effects. The main effects comprise changes in pi, hydration, solubility, viscosity of solutions, biological activity, and reactivity of a.a. residues. 

Denaturation For a nucleic acid or protein, the loss of tertiary and secondary structure so that the polymer becomes a random coiL For DNA, this change involves the separation of the two strands. Denaturation can he induced by heating and hy certain changes in chemical environment. It can also he stated as the disruption of hydrogen bonds and other weak forces that maintain the structure of a globular protein, resulting in the loss of its biological activity. 

In addition to chemical reactions, the isokinetic relationship can be applied to various physical processes accompanied by enthalpy change. Correlations of this kind were found between enthalpies and entropies of solution (20, 83-92), vaporization (86, 91), sublimation (93, 94), desorption (95), and diffusion (96, 97) and between the two parameters characterizing the temperature dependence of thermochromic transitions (98). A kind of isokinetic relationship was claimed even for enthalpy and entropy of pure substances when relative values referred to those at 298° K are used (99). Enthalpies and entropies of intermolecular interaction were correlated for solutions, pure liquids, and crystals (6). Quite generally, for any temperature-dependent physical quantity, the activation parameters can be computed in a formal way, and correlations between them have been observed for dielectric absorption (100) and resistance of semiconductors (101-105) or fluidity (40, 106). On the other hand, the isokinetic relationship seems to hold in reactions of widely different kinds, starting from elementary processes in the gas phase (107) and including recombination reactions in the solid phase (108), polymerization reactions (109), and inorganic complex formation (110-112), up to such biochemical reactions as denaturation of proteins (113) and even such biological processes as hemolysis of erythrocytes (114). 

That which we call a rose, by any other name would smell as sweet. The essence of the denatured state, in contrast, is rather more elusive. The difficulty stems, at least in part, from the wide variety of methods of inducing a protein to unfold. Some proteins appear to be natively unfolded that is, they remain unfolded in the cell under conditions in which they retain their biological activity (Plaxco and Gross, 1997 Wright and Dyson 1999 Dunker, 2002). Other proteins unfold only under the influence of changes in pH, high or low temperatures, or... 

Similarly to the above-mentioned entrapment of proteins by biomimetic routes, the sol-gel procedure is a useful method for the encapsulation of enzymes and other biological material due to the mild conditions required for the preparation of the silica networks [54,55]. The confinement of the enzyme in the pores of the silica matrix preserves its catalytic activity, since it prevents irreversible structural deformations in the biomolecule. The silica matrix may exert a protective effect against enzyme denaturation even under harsh conditions, as recently reported by Frenkel-Mullerad and Avnir [56] for physically trapped phosphatase enzymes within silica matrices (Figure 1.3). A wide number of organoalkoxy- and alkoxy-silanes have been employed for this purpose, as extensively reviewed by Gill and Ballesteros [57], and the resulting materials have been applied in the construction of optical and electrochemical biosensor devices. Optimization of the sol-gel process is required to prevent denaturation of encapsulated enzymes. Alcohol released during the... 

Compared to other HPLC techniques, RPC has a higher resolution power and allows protein analysis at low ionic strengths. On the other hand, it can be responsible for protein denaturation, loss of biological activity and interferences of hydrophobic contaminants [107]. 

When working with enzymes, proteins and other biological molecules it is often crucial to buffer the pH of the solution in order to avoid denaturation (loss of activity) of the component of interest (see Topic C3). Numerous buffers are used in laboratories for this purpose. One of the commonest is tris(hydroxy-methyl)aminomethane or TRIS which has a pK of 8.08. 

Some enzymes and enzyme systems are still active at the temperature of frozen storage (123-132). Such enzymatic activity, especially of proteases, may cause loss of biological activity of actomyosin and other muscle proteins. Products of such enzymatic activity, e.g. free fatty acids and formaldehyde, may effect a secondary denaturation of muscle proteins. 

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