I have purified a protein of unknown sequence that runs as a single peak on
gel filtration. An analysis on SDS-PAGE shows two bands. Before staining
the gel (coomassie) the upper of the two bands is already clearly visible
(~24kDa). The lower band only becomes visible after staining (12kDa). My
feeling is the two bands represent the same protein and the upper band has
something covalently attached (some sort of dye) such that the protein runs
erratically on SDS-PAGE and allows it to be visualized without staining.
Does anyone have any experience of this or have any idea what is attached to