Protein precipitation is a commonly used technique in downstream processing of biological products. There are several methods of precipitating proteins, including the use of ethanol or methanol solvents, non-ionic hydrophilic polymers like dextrans and PEGs, and adjusting the pH to the protein's isoelectric point. Important parameters for effective precipitation include temperature, pH, and protein concentration in solution. The precipitation process involves the nucleation of small protein aggregates between 0.1 and 10 micrometers in size, which then grow larger through attractive electrostatic and dipole forces between proteins.

1. Precipitation
Dr. Deepak Bhusare
Department of Microbiology
DB, ACS College, Bhokar.

2. Introduction
•Protein precipitation is widely used in downstream processing of biological
products.
•Hydrophilic and hydrophobic amino acid residues on the protein's surface.
•High hydrophobic amino acid have low solubility in an aqueous solvent.
•Charged and polar surface residues interact with ionic groups in the solvent and
increase the solubility of a protein.

3. Protein precipitation
•Nucleation phase: submicroscopic sized protein aggregates, or particles,
are generated.
• Particle size 0.1 µm to 10 µm.

4. Solvents Precipitation
•Ethanol or Methanol to a solution may cause proteins in the solution
to precipitate.
•the proteins can aggregate by attractive electrostatic and dipole forces.
•Important parameters: Temperature less than 0 °C to
avoid denaturation, pH and protein concentration in solution

5. Non-ionic hydrophilic polymers Precipitation
•Polymers: Dextrans and Polyethylene Glycols, are frequently used to
precipitate proteins.
•Attract water molecules away from the solvation layer around the
protein.
•This increases the protein–protein interactions and enhances
precipitation

6. Isoelectric (pI) precipitation
•At high pI protein possess negative charge.
•At low pI protein possess positive charge.
•The pI of most proteins is in the pH range of 4–6
•Mineral acids, such as hydrochloric and sulfuric acid are used as
precipitants

7. Thank You