③ Chromatography
- Chromatography offers a variety of methods to separate proteins based on charge, size,
hydrophobicity, and molecular recognition
A. Size exclusion (gel permeation or filtration) chromatography
1. The principle of separating proteins according to their hydrodynamic volume
2. Their molecular weight can be used if the size of the molecule to be separated is presumably different
from that of the contaminant proteins
3. The limitation is the largest sample volume suitable for an optimal separation is relatively small with
regards to the column size
4. This method has been successfully used for separation of other biomolecules, growth factors, tissue
plasminogen activator(TPA), and monoclonal antibodies
B. Ion exchange chromatography
1. It is dependent on the electrostatic interactions between the protein and charged groups on the exchangers
2. The nature of the ion exchange :
- Weak acid (carboxylmethyl, CM) vs weak base (diethylaminoethyl, DEAE)
- Strong (quaternary amine, Q) and quaternary aminoethyl, QAE)
3. The bound proteins are usually eluted with an ionic strength gradient or a pH gradient for strongly
bound proteins