Assessing Protein Purity

Determination of protein purity is crucial, as proteins are frequently used as therapeutic agents and reagents in many biochemical reactions. Additionally, purified protein is necessary for biophysical and structural studies. Assessing protein purity involves examining for impurities or demonstrating their absence. In our experience, a satisfactory answer is seldom obtained when biochemistry students are asked a common question on how to establish the purity of a given protein. This is not surprising, as no single technique firmly establishes protein purity. A combination of several techniques/approaches is needed for the assessment of protein purity. 
SDS-PAGE, 2-dimensional electrophoresis, mass spectral methods, and N-terminal sequencing are the front-line techniques used in the assessment of protein purity. Ignoring protein purity can result in erroneous interpretations in experimental results. This review describes the diverse methods employed to confirm protein purity.