Imagine that you have just finished a purification of your protein of interest (Protein X). You treat your samples with β-mercaptoethanol and run an SDS-polyacrylamide gel to analyze the purity of your protein prep. You included five known protein standards on your gel, and the results are as follows:
Protein standard mass (kDa)
Protein mobility
17
0.96
26
0.72
45
0.55
78
0.32
105
0.22
Table
1.
Based on its amino acid sequence, Protein X has an estimated molecular weight of 97 kDa. What relative mobility do you expect to see for Protein X on this gel?
You measure the actual mobility of Protein X as 0.15. Which of the following hypotheses most likely explains this discrepancy between the expected and actual mobility of Protein X?
Your gel shows a second band that you believe corresponds to a ligand binding partner for Protein X. This band shows a mobility of 0.68. What is the apparent mass of the protein ligand at this location?
