1,、 Precipitation method

The precipitation method is also known as the solubility method. The basic principle of purifying living macromolecules is to change certain properties of the solution based on the structural differences of various substances, leading to changes in the solubility of effective ingredients.

1. Salting out method

The salt precipitation method is based on the fact that the solubility of proteins in dilute salt solutions increases with the increase of salt concentration. However, when the salt concentration increases to a certain value, the water activity decreases, leading to the gradual neutralization of surface charges of protein molecules, the gradual destruction of hydration membranes, and ultimately causing mutual condensation and precipitation of protein molecules from the solution.

2. Organic solvent precipitation method

There are two reasons why organic solvents can reduce protein solubility: firstly, they have the same dehydration effect as salt solutions; Secondly, the dielectric constant of organic solvents is smaller than that of water, resulting in a decrease in the polarity of the solvent.

3. Protein precipitant

Protein precipitants only act on one or more types of protein precipitation, commonly including alkaline proteins, lectins, and heavy metals.

4. Polyethylene glycol precipitation

Water soluble non-ionic polymers such as polyethylene glycol and dextran sodium sulfate can precipitate proteins.

5. Selective precipitation method

According to the different stability characteristics of various proteins under different physical and chemical factors, appropriate selective precipitation methods can be used to denature and precipitate the heterologous proteins, while the active components to be separated exist in the solution, thus achieving the purpose of purifying the active components.