Recombinant human Follistatin isoform 2 is a polypeptide chain containing 217 amino acids with a predicted molecular mass of 32.3 kDa. Follistatin is a monomeric glycoprotein that binds to ligands of the TGF-β superfamily and regulates their activity. The biological activity of human Growth Hormone is measured by cell proliferation using Nb2-11 cells with an ED50 of 0.1-0.3 ug/ml in the presence of 7.5 ng/ml Activin A.