I am interested in a secreted protein and I express it in HEK cells. I see a band at a lower molecular weight (around 60 kDa) in the cell lysate, but a band at a higher molecular weight in the medium. (around 70 kDa). Could this be because of higher salt concentration in my cell culture medium? I used OPTIMEM medium, reduced serum to avoid excess albumen blot in my medium. I found a couple of references which say that higher salt can skew molecular weight interpretations.
It sounds like you are seeing albumin as you suspect. It generally migrates at 66kDa. If you provide some more details, you will likely receive more interesting suggestions. For example, are you visualizing the protein by western blot? Are you performing a step (e.g. TCA precipitation) to concentrate secreted proteins?
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