Hi Juan,

we found it difficult to do such experiments. Very often we found a considerable amount of proteins, that are nominally smaller than the cut-off, retained in the "larger fraction". This could be due to unspecific binding to the membrane or interactions with other proteins in the lysate. I agree with Markus - if you want to have a quantitative separation, rather use gel filtration. Good luck, Magdalena

I am aware of such two facts, precisely I need a quick and qualitative method to enrich basically with proteins of high molecular weight and then make a 1D or 2D electrophoresis. I ultracentrifuge my sample (1000000 x g) and I'm gonna try using detergents too, so much thanks for your advice!!. Do you (Magdalena and Markus) consider a good idea to use a reducing agent as DTT in additions to detergents previously to ultra-filtrate the sample?.