Problem with protein samples - No bands detected at all on gel (Feb/08/2010 )

Hi, I did SDS gels using Secretory Excretory Products (SEPs) from a parasite. I found even though my BCA showed that the sample contained protein, when I run the sample on a SDS gel no bands appear. Im looking for a reason for this. I run other samples on the same gel and they are fine. I am wondering could it be my sample as it has a high salt concentration in it. Also I used dopamine to obtain the SEPs could this interfere. I have used these samples on proteases assays and have detected activity so Im hoping it is not the BCA assay that is wrong. Any suggestions for possible reasons?
Thanks

Hi,
Did you do a solvent/buffer control in the BCA to control for background BCA turnover?
Good luck

you can try removing the salt by drop dialysis prior to treating with sds sample buffer.

also,

how are you detecting the protein in the gel? coomassie? silver? immunostain? something else?

your protein load may be too little to detect by the method you are using. if you are using silver, i have seen proteins that required a second round of silver staining to become visible.