Solubility Tests of Proteins

Solubility Tests is a type of biochemical test which is performed to check the ability of compounds to dissolve within a liquid solvent.

It is an essential test which can easily determine the size and polarity of unknown compounds and as well as the presence of acidic and basic functional groups.
The Solubility tests for proteins and amino acids are considered as the qualitative test which can detect the presence and absence of different proteins.

By detecting the solubility of proteins we can gather information regarding their functionality.
The protein solubility in aqueous buffers depends on the distribution of hydrophilic (having a strong affinity for water) and hydrophobic (lacking affinity for water) amino acid residues on the surface of proteins.
Hydrophobic residues are predominantly found in the globular protein core, but some exist in patches on the surface.

Proteins that have high hydrophobic amino acid content on the surface have low solubility in aqueous solvents.
Charged and polar surface residues interact with ionic groups in the solvent and increase solubility.
Solvent media has a great effect on protein solubility. These effects are: Ionic Strength, pH, Temperature, Dielectric Constant

Aim of Solubility Tests of Proteins

To detect the solubility of proteins in different solvents.

Principle of Solubility Tests of Proteins

The nitrogen present within the protein sample is proportional to the solubility of proteins, which remains in a soluble state under specific conditions. The amino acids of proteins are soluble in water while they are insoluble in non-polar organic solvents. The amino and carboxyl groups of amino acids helps the amino acids and proteins to accept and donate protons to the aqueous solution.

The protein solubility within a solvent is affected by different factors such as the molecular size, pH of the medium, hydration of the proteins, and the salting-in process. The addition of salts during the salting-in technique, generates an interaction between the surface ionic charges on the proteins and the electrolyte, which prevents the aggregation of protein particles. Depending on all of these factors, the solubility of the protein in different solvents might differ.

Requirements for Solubility Tests of Proteins

Reagent: Sample solution, Solvents (HCl, NaOH, Chloroform, Water)
Materials: Test tubes, Test tube stand, Dropper.