Recombinant protein activity is highly dependent on the assay performed due to the wide array of variables within a given experimental system. Reference standards provide an effective means of controlling for these variables across assays to determine the relative protein activity. By testing the material in question alongside a reference standard, the specific activity of the protein relative to the reference material can be determined.
The specific activity is reported in units (U) or international units (IU) when the reference material is recognized as a World Health Organization (WHO) international standard. Converting to units allows for a comparison of protein activity across multiple vendors and to ensure a consistent level of activity in an experimental system over time.
BioLegend often tests our recombinant proteins against commercially available reference standards, including WHO International Reference Standards, when available. Reference standards were obtained from the National Institute for Biological Standards and Control (NIBSC), a WHO collaborating center. The specific activity of these proteins can be found in the table below.