IGF-1 LR3 is an 83-residue recombinant analog of human insulin-like growth factor I (IGF-I). It comprises the complete 70-residue IGF-I sequence with arginine substituted for glutamate at position 3 (Arg3), preceded by a 13-residue N-terminal extension, MFPAMPLSSLFVN, derived from the N-terminus of porcine growth hormone. Like native IGF-I, it contains three intramolecular disulfide bonds.

The Arg3 substitution and N-terminal extension markedly reduce binding to IGF-binding proteins (IGFBPs) while largely retaining affinity for the type 1 IGF receptor (IGF1R), a receptor tyrosine kinase. In cell-based assays the analog has been characterized as more potent than native IGF-I, a difference attributed primarily to reduced IGFBP sequestration rather than increased receptor affinity.

IGF-1 LR3 is used in IGF1R signaling studies, including PI3K–Akt and MAPK pathway activation, IGFBP interaction assays, growth-factor supplementation of serum-free cell culture, and protein-folding research examining disulfide-bond formation. As a disulfide-bonded protein, it is sensitive to reducing agents and to repeated freezing and thawing in solution.

Research use only. This material is sold for in-vitro laboratory research and development purposes exclusively. It is not a drug, food, or dietary supplement, has not been evaluated by the FDA, and must not be used in humans or animals.