Specific Activity Calculator

What is meant by a “unit” of protein activity? The biological activity (ED ₅₀) (or “unit”) for each recombinant protein is available on the certificate of analysis. The ED ₅₀is 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 ED ₅₀to specific activity is:

Please note that MCE 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.

Most MCE recombinant proteins are tag-free. Protein tags are useful in some situation.

1. a. Protein tags are useful for protein purification.
2. b. Tags are used for protein detection in Western blot or ELISA when the specific antibodies are not available.
3. c. The Fc tag stabilizes molecules, which may increase the half-life of the linked products. Since the Fc fragment tends to dimerize, it helps the linked protein, particularly receptors, to form biologically active dimers. Protein tags generally do not affect the protein’s activity. For some small tags, such as the His-tag, do not need to be removed. There are more than 100 structures of His-tagged proteins in the Protein Data Bank, which indicates that the small His tags often do not usually interfere with correct protein folding. Additionally, tested activity results are listed on our protein web pages. If you have concerns about tags interfering with protein activity and there is no activity data online, please feel free to contact us for latest information at [email protected].