Fibroblast growth factor-21 (FGF21) belongs to the large FGF family which has at least 23 members. Along with FGF-19/15 and FGF-23, FGF-21 is categorized as a member of the atypical FGF subfamily, as it must be complexed to the Klotho co-receptor in order to bind to the FGF receptors and activate the downstream signaling pathway. FGF family members possess broad mitogenic and cell survival activities and are involved in a variety of biological processes including embryonic development, cell growth, morphogenesis, tissue repair, tumor growth and invasion.

> 97% as determined by SDS-PAGE; > 97% as determined by HPLC