Using urea in ion exchange chromatography of proteins - (May/11/2008 )

Hi all,
do you have any experience with using urea in protein sample for ion exchange chromatography?
It is difficult to dissolve completely the proteins of my interest - some (membrane) proteins associated with cytoskeleton. Therefore I use urea – the final concentration is usually 2 - 4M in protein sample, that is used directly for (an)ion exchange chromatography. Urea is non ionic detergent, so it should not influence (decrease) binding proteins to column, is it right?
If I use an other sample with 4M urea and then the same without urea, usually I can see a little bit higher peak in flow through at the sample with urea. That means, the urea probably decreases binding some proteins to column or ? What is your experience?

Thanks in advance for giving me suggestions.
victor

urea will expose buried charges and will, thus, influence the binding and elution profiles of the proteins.