The IGFs, or insulin-like growth factors, are polypeptide growth factors known for their ability to stimulate the proliferation and survival of various cell types, including those found in muscle, bone, and cartilage tissue when studied in vitro. While primarily synthesized in the liver, different tissues produce IGFs at specific times. Belonging to the Insulin gene family, which also includes insulin and relaxin, IGFs share structural and functional similarities with insulin but exhibit significantly greater growth-promoting activity.

IGF-II expression is influenced by placenta lactogen, while growth hormone regulates IGF-I expression. Both IGF-I and IGF-II signal through the tyrosine kinase type I receptor (IGF-IR), though IGF-II can also utilize the IGF-II/Mannose-6-phosphate receptor pathway. Mature IGFs are formed through proteolytic processing of inactive precursor proteins, which contain N-terminal and C-terminal propeptide regions.

Recombinant Human IGF-I and IGF-II are globular proteins composed of 70 and 67 amino acids, respectively, and each contains three intra-molecular disulfide bonds. IGF-I LR3, a recombinant analog of Human IGF-I, features the complete IGF-I sequence with an Arginine substitution for the third position Glutamic acid, as well as a 13-amino acid N terminus peptide extension. Engineered for enhanced biological potency in vitro, IGF-I LR3 boasts an extended half-life and reduced binding affinity to native proteins within the body, making it well-suited for both research purposes and large-scale culturing. Recombinant Human IGF-I LR3 is a single, non-glycosylated polypeptide chain weighing 9.1 kDa and consisting of 83 amino acid residues.