Salting-out salts

An analogy can be drawn between pericyclic reactions in water and under high pressure. Water s internal pressure on hydrophobic substrates acts on the volume of activation of a reaction in the same way as an externally applied pressure does. Thus, the internal pressure of water influences the rates of pericyclic reactions in water in the same direction as external pressures. The use of salting-out salts will further increase the rate of pericyclic reactions. Recently, Kumar quantified the relationship between internal pressure and the rate of the aqueous Diels-Alder reaction. A linear relationship between the two was observed.5... 

Salting-out salts (Na2S04, NaCl, MgS04) Surface tension increase Weak binding Stabilize globular proteins and precipitants of native and denatured proteins... 

Solubility — Salting Out Salting out fractionation Solubility under different solvent conditions, pH, ionic strength, hydrophobic interactions. 

Measurement of the inactivation rates of AMDH were performed under various conditions of salt types, salt concentrations, temperatures, and buffers (Mevarech and Neumann, 1977 Pundak et al, 1981 Zaccai et al., 1986b, 1989 Hecht andjaenicke, 1989a). It was found that (1) the inactivation process is of first order (which means that only one active form of the enzyme exists), (2) the rate constant for inactivation increases as the salt concentration decreases, (3) the temperature dependence of the rate constants of inactivation depends on type of salt, and (4) the dependence of the rate constants on salt type follows the Hofmeister series (von Hippel and Schleich, 1969), being lower for salting-out salts. The different models for the role of the salts in the stabilization of the AMDH will be discussed in Section IV,G. 

Numerous compounds can provide general cryoprotection to proteins, when used at concentrations of several hundred millimolar. These include sugars, polyols, amino acids, methylamines, and salting-out salts (e.g., ammonium sulfate) [59,61,68-70]. Based on the results of freeze-thawing experiments with LDH and PFK and a review of the literature on protein freezing. Carpenter and Crowe [59] have proposed that this cryoprotection can be explained by the same universal mechanism that Timasheff and Arakawa have defined for solute-induced protein stabilization in nonfrozen, aqueous solution (reviewed in [4,70,78,79]). 

Salt precipitation with ammonium sulfate is the most commonly used of these methods. Different ions were ranked according to their lyotropic/chaotropic ( salting-out / salting-in ) effects by Hoffineister in 1888 (Table 3). Ammonium sulfate ranks among the most effective precipitating salt and is convenient to use because of its high solubility which is only minimally dependent on temperature (7). 

On the basis of kinetic data and of the fact that the Diels-Alder reaction is accelerated in aqueous medium by adding salting-out salts (LiCl, NaCl) and retarded by adding salting-in salts (LiC104, guanidinium chloride), Breslow su ested that the acceleration and the increased selectivity of the reaction are ascribable to hydrophobic packing of diene and dienophile. 

HIC is most strongly affected by the specific effects of the salts. To enhance protein binding to the resin at the weakly hydrophobic ligand (such as phenyl group), a salting-out salt is required. Ammonium sulphate ((NH4)2S04) and sodium sulphate (Na2S04) are the most-utilized... 

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