Fibroblast Growth Factor 21 (FGF-21) belongs to the fibroblast growth factor family and functions through binding its obligatory co-receptor KLB (beta-Klotho) Expression of FGF-21 is regulated by metabolic conditions notably being induced downstream of hepatic HMG-CoA synthase 2 (HMGCS2) activity and produced by tissues such as brown adipose tissue under cold stress Mechanistically FGF-21 promotes glucose uptake into adipocytes by specifically facilitating expression of glucose transporter SLC2A1 (GLUT1) but not SLC2A4 (GLUT4) Recombinant Rat FGF-21 consists of 180 amino acids and exhibits limited binding affinity towards heparin Rat FGF-21 shares amino acid sequence identities of 81% and 92% with human and mouse orthologs respectively and retains biological activity across human and mouse cells Such recombinant proteins (e g Human IL-2 P60568 residues 21-153 His-tagged expressed in E coli) are routinely utilized as tools for metabolic and endocrinology research