What is protein purification used for?

The aim of protein purification is to isolate one or a few target proteins from a complex mixture for subsequent use. 

Protein purification has a wide range of laboratory applications as well as commercial applications. Laboratory applications include the study of structure, function, and post-translational modifications of proteins. Commercial applications include the preparation of certain biopharmaceuticals such as insulin, nutritional proteins such as soy protein isolate, and enzymes such as lactase.

Protein purification may also be used to extract bi-products such as host cell proteins that are a potential health hazard.