For research use only. Not for human or animal consumption.
Compound Monograph
IGF-1 LR3 (Long R3 analog): Mechanism
IGF-1 LR3 (Long Arg3 IGF-1) is an engineered analog of insulin-like growth factor 1 used widely as a research reference because of its extended activity relative to the native protein. This monograph describes its structural modifications, its receptor binding, and the binding-protein interaction that gives it its distinctive half-life. All content is for laboratory research use only and characterizes mechanism, not any consumer application.
Molecular class and structure
Native human IGF-1 is a 70-amino-acid single-chain protein structurally homologous to proinsulin. IGF-1 LR3 is an analog of this protein carrying two engineering changes that together define it: an amino-acid substitution within the mature sequence and an added N-terminal peptide extension.
The result is an 83-residue polypeptide (the 70-residue IGF-1 body plus a 13-amino-acid N-terminal extension) with a molar mass of approximately 9.1 kDa. The two modifications are described in detail below.
The Arg3 substitution and N-terminal extension
The 'R3' in the name denotes substitution of the native glutamic acid at position 3 of the mature IGF-1 sequence with an arginine residue (Arg3). The 'Long' (L) denotes a 13-amino-acid N-terminal extension appended ahead of the mature sequence.
Both modifications share a single functional purpose: to reduce the analog's affinity for the family of IGF binding proteins (IGFBPs). Native IGF-1 circulates largely bound to IGFBPs, which sequester it and regulate its availability. By weakening IGFBP binding, IGF-1 LR3 remains comparatively more available as free peptide in model systems, which is the basis of its markedly longer functional half-life — reported on the order of many hours versus minutes for native IGF-1.
Arg3: glutamate-to-arginine substitution at position 3 of mature IGF-1.
IGF-1 LR3 retains the receptor-binding face of native IGF-1 and acts as an agonist at the type 1 IGF receptor (IGF-1R), a receptor tyrosine kinase. Ligand binding triggers receptor autophosphorylation and recruitment of adaptor proteins, activating the downstream PI3K/Akt and Ras/MAPK signaling cascades that IGF-1R engages.
Because of structural homology, IGF-1 also has lower-affinity cross-reactivity with the insulin receptor, and the LR3 analog is studied with that cross-reactivity in mind. The core mechanistic point in the literature is that LR3 preserves IGF-1R agonism while altering the pharmacokinetic profile through its IGFBP-evading modifications.
Why the modifications are studied
The reduced IGFBP binding makes IGF-1 LR3 a useful research tool: in cell culture, IGFBPs secreted into media can blunt the activity of native IGF-1, whereas LR3's diminished binding gives more consistent receptor engagement. This is why the analog is a common reference in in-vitro signaling and proliferation assays, where reproducibility of receptor stimulation is the experimental goal.
Laboratory handling and verification
As a larger polypeptide, IGF-1 LR3 is handled with attention to its sensitivity to freeze-thaw cycling and to adsorption losses; carrier-protein-containing diluents are commonly used in research handling. Storage follows the protein's stability profile.
Each Kairo Labs lot is verified to the lot with a Certificate of Analysis documenting identity and purity, so the analog's modifications and grade are confirmed before use in research.
Frequently asked
What do 'Long' and 'R3' mean in IGF-1 LR3?
'R3' is the substitution of arginine for the native glutamic acid at position 3 of mature IGF-1. 'Long' is a 13-amino-acid N-terminal extension. Together they weaken IGF binding-protein affinity.
How does IGF-1 LR3 differ from native IGF-1?
It adds an N-terminal extension and an Arg3 substitution that reduce IGFBP binding, producing greater free-peptide availability and a longer functional half-life while retaining IGF-1R agonism.
What receptor does IGF-1 LR3 activate?
It is an agonist at the type 1 IGF receptor (IGF-1R), a receptor tyrosine kinase signaling through PI3K/Akt and Ras/MAPK, with lower-affinity cross-reactivity at the insulin receptor.
Why is IGF-1 LR3 used in cell-culture research?
Its reduced IGFBP binding gives more consistent receptor engagement in media where secreted IGFBPs would otherwise blunt native IGF-1, improving assay reproducibility.
How is the analog verified?
Each Kairo Labs lot ships with a Certificate of Analysis verified to the lot, documenting identity and purity so the analog's modifications and grade are confirmed before research use.
Research Use Only. All products and information referenced by Kairo Labs are intended strictly for laboratory research and educational purposes. They are not for human or animal consumption, and not for diagnostic, therapeutic, or clinical use. This content describes mechanisms, molecular properties, and handling as studied in the scientific literature; it is educational, not medical advice, and not a recommendation to use any compound in humans or animals. Researchers are responsible for handling all materials in accordance with applicable laws, regulations, and institutional safety protocols.
