Proteins stability salt effects

Protein conformation is also markedly affected by the concentration and type of ionic species present. In solution, individual salt effects can be either stabilizing or denaturing [26,27], These effects correspond to the Hofmeister lyotropic series ... 

Properly folded native proteins tend to aggregate less than when unfolded. Solution additives that are known to stabilize the native proteins in solution may inhibit aggregation and enhance solubility. A diverse range of chemical additives are known to stabilize proteins in solution. These include salts, polyols, amino acids, and various polymers. Timasheff and colleagues have provided an extensive examination of the effects of solvent additives on protein stability [105]. The unifying mechanism for protein stabilization by these cosolvents is related to their preferential exclusion from the protein surface. With the cosolvent preferentially excluded, the protein surface is... 

Commercial wines are commonly tested for protein stability. Wine proteins, upon denaturation by heat or cold, may cause cloudiness and unsightly deposits after bottling. In addition, proteins may combine with iron and copper salts to form flocculate material in bottled wines. The reaction and absorption of proteins on bentonite is an effective means of removing protein from wines (109, 110, 111). Therefore, fining wines... 

Once a range of suitable pH and ionic strength are selected, the effect on protein stability is evaluated for the final selection of an optimal formulation pH. Only when the optimal pH and addition of common salts do not render the desired solubility are other additives considered. This adds to the complexity of the formulation and the challenge of maintaining stability. Recently, an empirical approach to determine protein phase diagrams using various biophysical techniques has been used to facilitate identification of optimal formulation conditions (Fan etal., 1995). 

The ions to the left in the series exert a stabilizing effect on proteins. The ions to the right may bind to the protein surface and thereby destabilize the protein. The effect of the ions is additive. Ammonium sulfate is a stabilizing salt often used for precipitation of proteins (2-3-M solution). Gdn-sulfate is a stabilizing salt, while Gdn-chloride is a strong denaturant. 

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