What is the precipitation of proteins?
Protein precipitation is a method used for extraction and cleaning proteins held in solution. Large, complex molecules, proteins generally have parts that have a negative electric charge and parts that have a positive charge, as well as hydrophilic and hydrophobic parts. There is a tendency for proteins in a cluster solution together and precipitation due to the attractiveness of the negative and positive parts of molecules and the attraction of hydrophobic parts. However, an attack to this tendency is that in aqueous solution of water molecules that are polar, they will tend to arrange around protein molecules due to electrostatic attraction between the opposite parts of water and protein molecules. This results in the protein molecules to be kept apart and remain in the solution, but there are different methods for achieving proteins.
The most commonly used method of clotting of proteins is the addition of salt solution, techniques often referred to as "salting". The most commonly used salt is withAmmonium. The interaction of salt ions of water molecules removes the water barrier between the protein molecules, allowing the hydrophobic parts of the protein to come into contact. This results in the protein molecules aggregates together and are made from solution. In general, the higher the molecular weight of the protein, the lower the concentration of salt, which is necessary to cause clotting, so it is possible to separate a mixture of different proteins in a solution by gradually increasing the salt concentration, so different proteins collide in different stages, which is known as fractional precipitation.
The solubility of the protein in the aqueous medium can be reduced by introducing an organic solvent. This results in a decrease in The Dielectric Constant, which in this context can be considered a degree of solvent polarity. Reducing polarity means that there is less tendency to group solvent molecules around the protein, so there are less water barriers between the proteins and the greater tendency toCoating proteins. Many organic solvents interact with the hydrophobic parts of the protein molecules, causing denaturization; However, some such as ethanol and dimethylsulfoxide (DMSO) are not.
Although proteins may have negative and positive parts, they often have a generally positive or negative charge that changes according to the pH and maintains them separately by electrostatic repel. In acidic conditions, with low pH, proteins tend to have a general positive charge, while at high pH the charge is negative. The proteins have a temporary point at which there is no overall charge - it is known as an isoelectric point and for most proteins lies in the pH of 4-6. The isoelectric point for dissolved protein can be achieved by adding acid, usually chlorocoloric or sulfuric acid to reduce the pH to a suitable level, allowing the proteins to be clotching and clotting. The disadvantage of this method is that acids tend to denature protein but often used to removeundesirable proteins.
Other methods of protein precipitation include non -ion hydrophilic polymers and metal ions. The first reduces the amount of water available to create a barrier between proteins molecules, allowing them to cluster and clot. Positively charged metal ions can connect with negatively charged parts of protein molecules, reducing the tendency of protein to attract a layer of water molecules around it, which again allows protein molecules to interact with each other and precipitate from solution. Metal ions are even effective even in very diluted solutions.