A simple, cheap and fast method is to put your protein solution into a dialysis bag (e.g. with 10 KDa cutoff), place it over a bed of polyethylene glycol (PEG) and cover it with more PEG. Although frequently called "reverse dialysis" it is actually the osmotic force that drives water out of the dialysis bag. Then, simply follow the decrease in volume over the next few hours and recover the sample when the extent of concentration is satisfactory.

I hope this helps. Good luck!

Dear Laura

The procedure depends on few characters

1. Position of protein in the cell, or cell membrane

2. simple or conjugate protein

3. Composition of a.a.

Depending on this you can go for Chromatographic separation.

It´s a simple protein

You can either use dialysis or you can buy protein concentration columns. The protein concentration spin columns come with different pore sizes. You can choose the one that you want based upon the molecular weight of your protein. We use protein concentration columns from Millipore.

Here's a link with the information about Millipore's protein concentration columns http://www.millipore.com/userguides/tech1/www-uf

Good luck!

A simple, cheap and fast method is to put your protein solution into a dialysis bag (e.g. with 10 KDa cutoff), place it over a bed of polyethylene glycol (PEG) and cover it with more PEG. Although frequently called "reverse dialysis" it is actually the osmotic force that drives water out of the dialysis bag. Then, simply follow the decrease in volume over the next few hours and recover the sample when the extent of concentration is satisfactory.

I hope this helps. Good luck!

I assume you are asking about concentrating a protein following dialysis?

The methods outlined above should work in most situations. In cases where you have a very large volume of a dilute protein solution (say, where your dialysis bag leaked!) then a concentrative chromatography step (e.g. ion exchange, HIC) may be faster/more effective. Of course, you may need to re-exchange the buffer afterwards.

I thank you for all suggestions given. I am looking for an inexpensive method, the method for dialysis is the ideal, but I have questions about the selection of dialysis buffers used and the treatment that should be given prior to the bags dialysis, because sometimes they may contain contaminants such as heavy metals or other substances that may interfere with the activity of the protein concentrate. Someone could suggest a protocol or a review on the subject?

I use Slide-A-Lyzer dialysis cassettes. Very simple and reduces the risk of lost sample compared to typical dialysis tubing, plus they come in many different sizes. Dialysis won't concentrate your protein though, and it's mainly to remove salts and low MW contaminants. Choose the dialysis buffer based on your next downstream application. For example if your next procedure after dialysis is size-exclusion chromatography, dialyze your protein against the running buffer to be used in your column. Afterwards try the Millipore concentrators, and choose the appropriate size-cutoff for your protein, they worked well for me, except my expression yields were terribly low so there wasn't much to concentrate :( Oppositely, you can concentrate first using ammonium sulfate or similar method, then dialyze or use a desalting column (such as Zeba spin) to remove salts (although this will dilute your sample a bit).