I wanted to use proteinase K to treat conditioned media in order to determine if a protein factor is responsible for the effect seen when CM is used on cells. I have come across various protocols in the literature. Does anyone have experience in using proteinase K for this purpose? I am trying to find the best way to determine if the PK is working. I have treated with 200ug/ml and neutralized with 5mM Pefablock but then when using this on my cells they all died. I think the Pefablock lowered the PH of my conditioned media. I then tried using 10ug/ml followed by heat inactivation but I need to find an assay that will prove that this concentration in my conditioned media actually degraded the proteins. Any advice will be appreciated.