Protein cold denaturation

Table V shows the results of this analysis for the Pn-helix fraction of several proteins denatured by heat, cold, acid, and Gdm HCl/urea. There is rather good consistency among the estimated Pn-helix contents for proteins denatured by a given agent, except for acid-denatured proteins, which show more variability. The chemically denatured proteins have 30 5% Pn-helix content near 0°C. At the other extreme, heat-denatured proteins have Pn-helix contents near 0%, with lysozyme having the highest value (8%). Although there are only two examples of cold-denatured proteins in Table V,2 they both have Pn-helix contents of about 20%. Acid-denatured proteins have Pn-helix contents ranging from 0 to 16%.

Precipitation by ethanol in the cold was used effectively by J.Mellanby in 1908 to obtain diptheria antitoxin two years later Hardy and Gardiner reported the precipitation of plasma proteins by cold ethanol or acetone. The resulting proteins remained soluble in water, i.e. they were not denatured, and subsequent estimation of protein as nitrogen was helped by the use of nitrogen-free precipitants. Separations using organic solvents were considerably extended by Edsall,... 

Hydrophobic effects are thus of practical interest. If we accept the goal of a simple, physical, molecularly valid explanation, then hydrophobic effects have also proved conceptually subtle. The reason is that hydrophobic phenomena are not tied directly to a simple dominating interaction as is the case for hydrophilic hydration of Na+, as an example. Instead hydrophobic effects are built up more collectively. In concert with this indirectness, hydrophobic effects are viewed as entropic interactions and exhibit counterintuitive temperature dependencies. An example is the cold denaturation of globular proteins. Though it is believed that hydrophobic effects stabilize compact protein structures and proteins denature when heated sufficiently, it now appears common for protein structures to unfold upon appropriate cooling. This entropic character of hydrophobic effects makes them more fascinating and more difficult. 

Ammonium sulfate, (NH4)2S04, is the most commonly used compound for salting out of proteins because it is very soluble (706 g/L) and has four ionic charges per molecule. Precipitations are generally performed slowly with cold solutions to minimize protein denaturation due to the heat... 

Protein denaturation can be due to physical reasons, e.g. heat (Figure 8.42), cold, mechanical forces, radiation or influence of chemical factors (acids, alkali, salts, solvents, surfactants, oxidants, heavy metals, chelating agents). 

F. Franks, R.H.M. Hatley and H.L. Friedman, The thermodynamics of protein stability. Cold denaturation as a general phenomenon, Biophys. Chem., 1988, 31, 307-315. 

Alexandrescu AT, Rathgeb-Szabo K (1999) An NMR investigation of solution aggregation reactions preceding the misassembly of acid-denatured cold shock protein A into fibrils. J Mol Biol 291 1191-1206... 

Nowadays, most breakfast cereals are made either by original traditional processes or by using alternative extrusion methods. Commercial flakes, shreds, and oven-puffed cereals could be alternatively manufactured via extrusion. There are two major types of extrusion processes cold and thermoplastic. Cold extrusion is almost exclusively applied for production of pasta products (Chapter 10), whereas thermoplastic extrusion is used for manufacturing breakfast cereals and snack foods (Chapter 12). Undoubtedly, the most popular and versatile extrusion process is thermoplastic, defined as the combination of heat and mechanical shear to enhance starch gelatinization and dextrinization, protein denaturation, and inactivation of microorganisms, enzymes, and antinutritional factors. The changes in the properties of the starch and proteins result in the formation of a plastic material that could be formed and/or restructured into desired configurations. 

At l i the protein again undergoes unfolding with heat adsorption ( heal denaturation ). Cold and heat deiiaturation therefore occur with opposite heal effects and define the thennal stability range (/ii -T ) of the native conformation. 

Because temperature shifts may also influence the packing quality, the temperature should not be changed during the chromatographic step and the packing of the column should be done at the operation temperature. To prevent the denaturation of sensitive proteins, the chromatography is carried out in a cold chamber (or cabinet). For this purpose the column packing has to be performed at the same ambient temperature (store the gel before use at the same temperature ). 

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