Why does my peptide run above its size after incubation with plasma - (Jun/21/2007 )

Hi,

Does any one can explain Why my peptide runs above its size after incubation with plasma on tris-tricin gel?

My peptide is 3.5 kDa. I run sample on 18 % tris-tricine gel in denaturing and reducing condition. Pure peptide is clear and flat band but peptide band is narrow and above its original size position after incubation with plasma.
I incubate peptide with plasma and directly dilute with sample buffer for loading to the gel.
Do I need to do any step to extract peptide from plasma before running gel? What should I do?

Your help is highly appreciated.

plasma contains salts and a lot of proteins. these factors can affect the running of the lane of the sample and those next to it.

if you can separate your peptide from the rest after plasma treatment, then you probably should.