Dear Margarita you can do dialysis and filtration through certain molecular cutoff range after that lyophilized the solution 

Hi,

I would try a vacuum chamber in this case. If you do not have an electric one you may use a cheap desiccator. This usually has a valve that can be connected to a water stream which generates the vacuum. Be careful that your proteins do not dry too much, otherwise you may not be able to re-dissolve them.

Regards

you are right karim

The best way to discriminate among a huge amount of proteins, the level of a low abundance protein is to used directly the soluble extract, and to detect the protein by some specific antibodies by western blot. If this method doesn't work, it would be difficult that those levels of protein precipitates properly by any whole precipitation method as TCA, or acetone, and to redissolve them. Any case, just try to use different concentrations of ammonium sulphate, that is a better agent for proteins.

Any case you can try other methods.

1.- Cooling 2.- pH adjustment 3.- Addition of solvents such as acetone and ethanol 4.- Addition of anti-chaotropic salts such as ammonium sulphate and / or sodium sulphate 5. Addition of chaotropic salts such as guanidine hydrochloride and / or urea 6.- Addition of biospecific reagents as in immunoprecipitation.

This last method would be very helpful if you have an specific antibody conjugated with any tracer, biotin, zinc finger, etc.that would allow recover of the complex protein-antibody.

Whilst I agree with the other suggestions made, I find that freeze-drying the supernatants to reduce the sample volume is an excellent way of concentrating samples whilst maintaining integrity of the protein. The sample can be reconstituted in a much smaller volume and then precipitated if needed, to remove salt and other impurities. I also like the centrifugal filters, which are much quicker but great care is needed to resuspend the proteins from the filter membrane afterwards. If there is a possibility of clogging, get a filter which is shaped in a 'V' configuration as this minimises problems of clogging.

Freeze and drying could be a nice method, as it may be centrifugal filter, but it always depend on the level of expression and properties of your particular protein. In many low level expression and low solubility proteins, those methods do not allow for a recovery form the precipitate or the filter. And the amount of salt and other components of the media requires a precipitation step in any case.

Thank you for your recommendations! I will try to implement them and let you know!