I have been producing some cutinase enzyme using bioreactors.

In order to concentrate my enzymes and increase the activity I tried to concentrate them using a Ni-sepharose chromatography column and the buffer that I used to elute the proteins is an imidazole buffer (250 mM)

after the concentration I measured the cutinase activity of my proteins on P-nitrophenyl-butyrate and I found a good activity

but when I put the concentrated proteins on a sds gel I don't see anything and also the bradford and Nanodrop test shows that I do have a small amount of protein.

Is it possible that the activity I found after the concentration is the effect of the imidazol and not my protein?

best,

Wissal