I am using Protease Inhibitor Cocktails (VWR_M221-1ML). I reconstituted the inhibitor, but I am not sure how much of the protease inhibitor do I add to my sample. I am preparing the sample for a metabolic panel analysis.
Protease inhibitor cocktails generally specify the amount to add. For instance, a 100X solution should be added in a 1:100 ratio by volume. I believe that is the case for the one you are using.
Dear Hatem, as far as I know, protease inhibitor cocktails should be added to lysis buffers just before homogenize cells or tissue samples with. Otherwise, the release of lysosomal enzimes (or any other intracellular protease) would degradate your sample proteins. Serum, however, does not contain proteases you may worry about. As Adam said the right amount of a protease inhibitor cocktail should be given by its stock concentration, but working on serum samples, I wouldn't use it.
Read the sheet came along with the vial. Do not discard, keep in notebook always.