Some non-ionic polymers (e.g. chitosan and polyethylene glycol) are also commonly used as protein precipitating agents. What is the principle of protein precipitation resulting from the addition of these polymers? Is this type of precipitation reaction a reversible or non-reversible precipitation?
Protein precipitation by these non-ionic polymer is based on the principle of steric hindrance. These polymers compete with proteins (Mahadevan, 1992) for space in the solvent. Congestion caused by the physical presence of surrounding polymers force the proteins to exclude from region occupied by the polymers and concentrate together until their solubility is exceeded (Atha & Ingham, 1981). In this case, protein precipitation occurs.