protein solubilty, electric charge, (zeta potentiel), charge neutralization,...
In general, low ionic strength will reduce zeta potential bot not to the point where the hydrophobic effect will kick in. Before this any increase in ionic strength favors the number of protein molecules that the solvent can accomodate. Surpassing this level will promote the hydrophobic effect and solubility will be reduced.
High ionic strength favors hydrophobic interactions, which could lead to protein aggregation if hydrophobic patches are exposed on the surface of the protein.
The identity of the ions also must be considered. Some ions are chaotropic, meaning they can have a denaturing effect, which would tend to cause protein aggregation due to exposure of normally buried hydrophobic surfaces. Sodium chloride, for example, is mildly chaotropic.
thank you, for your question; I am working on dry legume proteins.
The high concentrations of mineral ions reduces the availability of water molecules in the solution, wish decreased protein hydration and increased hydrophobic interactions, so precipitation (salting out)
Thank you for your answer. and how about salting in at low ionic strenght ?
Low ionic strength implies solubilization, Application to the purification of proteins.
(Salting in), the ionic strength motivate the polar character of the protein( ionization) which can easily react with water
Thank you very much my teacher Dr Kuidri, I am grateful.
For the case of salting out, it is more or less clear, In addition to the charge neutralization, salt molecules are more soluble in water then protein molecules, so water prefer to react with water then the protein and protein dehydrate which lead to their precipitation….
Now, I would like to know how low ionic strength promotes ionization at the molecular scale. I think that the problem is about molecule charge also!!!!! Low ionic strength enhances protein chare (zeta potential) which improves protein solubility……
Thank a lot dear sir Kuidri,
Actually increasing salt concentration (starting from nothing) will decrease the zeta potential, which increases protein solubility. You should read my previous answer.
Salting in occurs with rod-like proteins with different charge at both ends (+-), called albumins. In the absence of free ions, these proteins will aggregate by ionic bond formation:
(+-) (+-) (+-)
(+-) (+-) (+-) etc.
Low concentrations of mineral ions will neutralise these charges and thereby break the salt bridges between protein molecules, the protein will go into solution. Sperical proteins without charge symmetry (globulins) on the other hand do not form such almost crystalline arrays, they are soluble even in distilled water.
Both albumins and globulins are salted out by high salt concentrations, as discussed above by Adam and Mohamed. Note that in the field of blood plasma protein isolation the definition of albumin and globulin is slightly different.
salting in is described by Debye- Huckle theory. Solvation usually decreases the ionic interaction of charged side chains and this is due to water's high dielectric constant or relative permittivity and high dielectric means the ions feel a smaller force. Adding salts decreases the dielectric of water and salts interact with the ionic side chains helping it stabilize.
Article Salt Bridge in Aqueous Solution: Strong Structural Motifs bu...
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