That depends - how much protein? What you intend to do with it? is there a specific size or is it a mixture of proteins?

Some options that come into mind:

- Precipitation with ammonium sulfate or in organic solvent , e.g. 80% acetone.

- Centricon/Amicon/Vivaspin centrifugation concentrator.

-  Spin columns

want to isolate specific protein from total soluble proteins on the basis of bioassay

OK, so do you want to concentrate before purification or to concentrate after purification?

Before purification

So you intend to do bio-assay on the concentrated protein? You can try differential precipitation with ammonium sulfate (AS). You start with ~40% AS mix in the cold and centrifuge. Keep the pellet and add AS to make 60% AS final in the soup, incubate at the cold and centrifuge. Again soup, to 80%, cold, centrifuge.

See more here

http://blog.dilyx.com/2013/03/a-protein-purification-classic-ammonium.html

Hope this helps

Yoram

thank you so much Yoram.