A mixture of proteins contains four different polypeptides, all in ~equal concentration, in solution with the following properties:
Protein Molecular Mass (kDa) Isoelectric point
A 45 4.5
B 77 6.0
C 28 4.1
D 14 10.7
A fraction of the protein solution is applied to a strong cation exchange column using a buffer at pH 8.0 with increasing [NaCl] from 0.05 M – 1.0 M. The chromatogram is shown below:
1. Based on the data presented, which of the following statements is true:
- Peak #1 is protein D
- Peak #4 is protein C
- Peak #3 is protein A
- Peak #4 is protein D
- Peak #2 is protein B
2. Since you know that the proteins are all present in approximately equal concentrations, the different relative peak areas tell you that:
- There are more neutral amino acids in protein #4 than protein #3
- There are more
aromatic amino acids in proteins #3 and 4 than in proteins #2 and 1 - There is more proline in protein #2 than in the others
- The proteins must all be derivatized with an absorbing group
- Some of protein #3 does not elute at even the highest NaCl concentration
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