a. You have recently discovered a novel protein having a predicted molecular weight of 55 kD based on the amino acid sequence and denaturing polyacrylamide gel analysis. After purifying this protein to homogeneity (100% purity), you carry out gel filtration chromatography using a size exclusion column containing Superdex S200 medium and a mobile phase approximating physiological pH and physiological ionic strength (native conditions). After careful comparison with standards (all of which are globular proteins that migrate as expected), you discover that the novel protein, for some reason, elutes with an apparent molecular weight of only 3 kD. Stranger still, when you re-run the eluted protein on another SDS-PAGE gel, you discover that it migrates as a 55 kD protein. What is the most likely explanation for this unusual behavior on the column?
a. You have recently discovered a novel protein having a predicted molecular weight of 55 kD based on the amino acid sequence and denaturing polyacrylamide gel analysis. After purifying this protein to homogeneity (100% purity), you carry out gel filtration chromatography using a size exclusion column containing Superdex S200 medium and a mobile phase approximating physiological pH and physiological ionic strength (native conditions). After careful comparison with standards (all of which are globular proteins that migrate as expected), you discover that the novel protein, for some reason, elutes with an apparent molecular weight of only 3 kD. Stranger still, when you re-run the eluted protein on another SDS-PAGE gel, you discover that it migrates as a 55 kD protein. What is the most likely explanation for this unusual behavior on the column?
