proteinprecipitation

Protein precipitation is a technique used to remove proteins from solution by converting them into an insoluble solid that can be separated by centrifugation or filtration. It is commonly employed to concentrate protein samples, desalt or desalt, and provide a preliminary purification before further methods such as chromatography or electrophoresis. Precipitation relies on lowering or disrupting protein solubility through changes in solution conditions.

Several precipitation strategies are routinely used. Salting out uses high concentrations of inorganic salts (for example ammonium sulfate) to compete for water molecules, reducing protein solubility and causing proteins to come out of solution. The salt type and saturation level influence selectivity and yield. Isoelectric precipitation adjusts the solution pH toward the protein’s isoelectric point, where the net charge approaches zero and solubility drops. Organic solvent precipitation employs solvents like ethanol or acetone to decrease dielectric constant and promote aggregation, though it can risk denaturation. Polyethylene glycol (PEG) precipitation uses polymer-induced volume exclusion to drive protein aggregation. Each method has trade-offs in yield, purity, and potential denaturation.

Process considerations include gradual addition of precipitant, careful temperature control, and subsequent separation of the solid by centrifugation. Redissolution of the precipitate often requires optimization of buffer composition, pH, ionic strength, and temperature. Protein precipitation is widely used in proteomics, biotechnology, and sample preparation workflows, but it can co-precipitate contaminants and may not be suitable for all proteins.