The biological activity (ED50) (or “unit”) for each recombinant protein is available on the certificate of analysis. The ED50 is defined as the protein concentration at which the activity is 50% of the maximum response and is reported in ng/ml. This method of expressing activity should only be used for proteins whose dose-response curves are sigmoidal in shape. The formula for converting the activity as an ED50 to specific activity is:
Please note that GenScript does not use the International Standard provided by WHO (National Institute for Biological Standards and control) for measuring recombinant protein activity. There is not a way to convert between these “International Units” and the ED50. The best way to compare the activity of recombinant proteins from different sources is to do the same bioassay side-by-side using the same system.