IGF-1 LR3 (Long R3 Insulin-Like Growth Factor-1) is a synthetic analog of endogenous IGF-1 engineered for extended plasma half-life and reduced insulin-like hypoglycemic activity. It is used in cell biology, anabolic signaling, and muscle physiology research. This overview covers its biochemistry, published research, and laboratory specifications for qualified researchers.
What Is IGF-1 LR3?
IGF-1 LR3 is an 83-amino acid analog of human IGF-1 featuring two key modifications: an N-terminal 13-amino acid extension (the “Long” component) derived from the IGF-1 signal sequence, and a glutamic acid-to-arginine substitution at position 3 (the “R3” component). These modifications dramatically reduce IGF-1 binding to IGF-binding proteins (IGFBPs), which normally sequester approximately 99% of circulating endogenous IGF-1. By reducing IGFBP affinity by approximately 1,000-fold, IGF-1 LR3 has approximately 2–3× greater potency at the IGF-1 receptor (IGF-1R) and a plasma half-life of approximately 20–30 hours versus 12–15 minutes for native IGF-1 in research models.
Mechanism of Action
IGF-1 LR3 activates the IGF-1 receptor (IGF-1R), a receptor tyrosine kinase (RTK) expressed ubiquitously in mammalian tissues with particularly high density in muscle, liver, and adipose tissue. Receptor activation triggers autophosphorylation of the β-subunit kinase domain and initiates signaling through the IRS-1/PI3K/Akt and MAPK/ERK pathways. PI3K/Akt signaling promotes protein synthesis via mTORC1 activation, inhibits protein degradation via FOXO transcription factor suppression, and supports cell survival through Bad phosphorylation. The reduced IGFBP binding of LR3 means a greater fraction of the administered peptide remains bioavailable for receptor engagement throughout the experiment duration.
Published Research Highlights
Francis et al. (J Mol Endocrinol 1992) first described the biochemical properties of IGF-1 LR3 and its reduced IGFBP affinity. The analog became a standard reagent for cell culture growth promotion, replacing serum in defined medium formulations for many mammalian cell lines due to its potent mitogenic activity. Research using IGF-1 LR3 has illuminated downstream signaling specificity: its preferential IGF-1R versus insulin receptor (IR) binding has made it useful for separating IGF-1R from IR pathway contributions in dual-ligand experiments. Muscle satellite cell proliferation, protein synthesis rate studies using stable isotope techniques, and adipocyte differentiation assays frequently employ IGF-1 LR3 as the growth factor stimulus.
Research Use Only. IGF-1 LR3 is supplied by Bastion Peptides strictly for in vitro and laboratory research purposes. Not for human or veterinary use.
Laboratory Specifications
| Parameter | Specification |
|---|---|
| Molecular Formula | C₄₀₀H₆₂₅N₁₁₁O₁₁₅S₉ |
| Molecular Weight | 9,117.54 Da |
| Structure | 83 AA; N-terminal 13-AA extension; Glu³→Arg³ substitution; 3 disulfide bonds |
| Purity | ≥99% (HPLC verified) |
| Third-Party COA | Janoshik Analytical — available on request |
| Storage | −20°C lyophilized; 4°C in solution (use within 7 days) |
| Appearance | White lyophilized powder |
Reconstitution Protocol
Reconstitute IGF-1 LR3 in 10 mM HCl or 0.1% acetic acid (acidified water) rather than plain water or PBS, as the peptide is prone to aggregation at neutral pH upon initial dissolution. Once dissolved in acidified solution, dilute to working concentration using the appropriate assay buffer (PBS, cell culture medium). Typical cell culture concentrations range from 10–100 ng/mL; higher concentrations may be used for receptor binding or signaling assays. Aliquot immediately after reconstitution and store at −80°C for long-term stability. The 3 disulfide bonds in the native fold require avoiding reducing agents.
Available Formats
Bastion Peptides supplies IGF-1 LR3 at 1mg per vial, HPLC verified to ≥99% purity with Janoshik COA per batch. View current inventory in the shop.
For research use only. Not approved for human therapeutic use. Researchers are responsible for compliance with all applicable local regulations.
