ok, here's a lab question, hopefully somebody can help me out. I tried purifying an overexpressed recombinant protein(a protein of interest fused with GST which binds glutathione) using glutathione beads. I ran this sample on SDS-PAGE and performed coomassie staining. I also performed Western blot on an aliquot of the same sample. However, the results were negative for coomassie staining and Western (like there were no bands at all, clean as a slate). The molecular markers in both worked fine. Positive control only worked for coomassie. Here's the catch, from the same sample, I aliquoted some for quantification of protein concentration (OD sample) and there were proteins in the sample. How come I can't detect this protein in coomassie and western when optical density says there is protein in the sample? some insights?