124. Таложење со готварска сол, магнезиум-сулфат, олово-нитрат, цинк-сулфат, бакар-сулфат и етанол

About

The precipitation of proteins is a type of qualitative reaction to demonstrate their presence by intervening in their structure. There are two types of protein precipitation: reversible and irreversible precipitation.

To an egg white solution, the following was added:

Test tube 1: solid NaCl (on the tip of a spoon)

Test tube 2: solid MgSO4 (on the tip of a spoon)

Test tube 3: aqueous solution of Pb(NO3)2

Test tube 4: aqueous solution of ZnSO4

Test tube 5: aqueous solution of CuSO4

Test tube 6: 96 % ethanol

The solutions are mixed/stirred and a formation of precipitate is noted in all test tubes.

Precipitation of proteins with NaCl and MgSO4

In this case, there are no significant changes to the macromolecule and its associated complex particles (micelles), so the precipitated protein can return to its original state. With an increase in the concentration of ions in the solution, the colloidal particles of the proteins become destabilized, making them more prone to precipitation (changes occur in the water layer of the micelles, some of the charged parts of the micelle are neutralized, etc.).

The charged and polar amino acids in proteins are surrounded by water molecules, which enable their solubility. In an aqueous solution of a protein with high ionic strength (achieved by adding NaCl or MgSO4), water molecules surround the charged ions from the salt and the proteins. At a certain ionic strength, there are more ions from the salt in the solution than solvent that enables the solubility of the protein. Therefore, the least soluble components in the solution, in this case, the proteins, precipitate.

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Credit

Deni Ingilizovski

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