Purity >95%, by SDS-PAGE under reducing conditions and visualized by Colloidal Coomassie? Blue stain. MW (theoretical): 19.4 kDa. The Recombinant Human IFN-alpha 4b (alpha 4) Protein from R&D Systems is derived from E. coli. The Recombinant Human IFN-alpha 4b (alpha 4) Protein has been validated for the following applications: Bioactivity.