Salting out specific protein - (Feb/23/2017 )

How does one find the saturation level of ammonium sulfate for salting out a specific protein of interest? I've goggled this but all I get is how to achieve a specific saturation level, not how to find the saturation level needed.  Thanks

Assuming you've checked through the literature and can't find anyone who has done this for your protein before, you'll just have to do by step-wise titration. It's impossible to predict with any reliability how a protein will behave during ammonium sulfate precipitation.

Start with a 30% ammonium sulfate cut. Centrifuge and assay pellet and supernatant for your protein (activity assay, gel, affinity column, etc). Assuming it's in the supernatant, add additional salt until 50% saturation and repeat. Then 70%, then 80%, etc. It's a bit laborious but if you do it correctly then you only have to do it once to find your answer.