IGF-1 LR3
Also known as Long R3 IGF-1, IGF-1 Long R3, LR3 IGF-1
IGF-1 LR3 (Long R3) is an engineered analog of insulin-like growth factor 1, modified to reduce binding-protein association. A research-use profile of the LR3 modifications and IGF-axis context.
IGF-1 LR3 is interesting precisely because of what was changed and why. It is an analog of insulin-like growth factor 1, and its name is a compact description of two deliberate engineering decisions: 'Long' for an added N-terminal extension, and 'R3' for an arginine swapped in at position three. Understanding those two edits is understanding the molecule.
This page focuses on that modification story and on the IGF signaling axis the parent hormone belongs to. It stays clear of outcomes and use; the substantive, verifiable content is the structural difference from native IGF-1 and the binding-protein interaction those differences target.
A single-chain polypeptide analog of IGF-1. Relative to native IGF-1 (70 residues) it carries two engineered changes: an arginine substituted at position 3 (the 'R3'), and a 13-residue extension added to the N-terminus (the 'Long' prefix) — giving an 83-residue chain.
The two LR3 modifications
Native IGF-1 is a 70-residue single-chain polypeptide. IGF-1 LR3 makes two changes to it. The 'R3' is a point substitution: the amino acid at position 3 is replaced with arginine. The 'Long' is an N-terminal addition: a 13-residue peptide extension is fused to the front of the chain. Together these produce an 83-residue analog that is structurally close to IGF-1 but not identical to it.
These are not cosmetic edits. Position 3 sits in the region of IGF-1 that contacts its binding proteins, so substituting it is a targeted change aimed at that interaction — the single most-discussed feature of the LR3 variant.
The IGFBP-evasion angle
In circulation, native IGF-1 is largely bound by a family of IGF-binding proteins (IGFBPs) that regulate its availability. The R3 substitution is understood, in the research literature, to reduce the analog's association with these binding proteins compared with native IGF-1. That reduced binding-protein interaction is the defining research characteristic of LR3 and the reason it is studied as a distinct tool rather than as a stand-in for IGF-1 itself.
It is worth being precise: 'reduced binding-protein association' is a description of a molecular interaction the modification was designed to alter. It is not a claim about any physiological result.
The IGF signaling axis it belongs to
IGF-1 and its analogs sit in the growth-factor signaling axis, acting through the IGF-1 receptor, a receptor tyrosine kinase. IGF-1 LR3 is grouped in performance and muscle-biology research because that axis is central to those fields. It is frequently studied alongside growth-hormone-axis compounds, which sit upstream of endogenous IGF-1 production, and alongside splice-variant-derived peptides like MGF that arise from the same gene family.
These are research areas the compound is associated with in the literature — not medical claims or intended uses.
Handling & storage
As a longer recombinant polypeptide it is supplied lyophilized and handled carefully: kept sealed, cold, and dry, reconstituted only when a protocol requires it, and protected from repeated freeze–thaw. Handle per accepted laboratory practice.
Verify a certificate by lot →Common questions
'R3' is an arginine substituted at position 3 of the chain; 'Long' is a 13-residue extension added to the N-terminus. Native IGF-1 has neither.
It is an 83-residue engineered analog rather than the native 70-residue hormone, and its position-3 change reduces association with IGF-binding proteins in the literature.
It describes the analog's reduced binding to the IGF-binding-protein family compared with native IGF-1 — a molecular-interaction property the R3 modification targets, not a physiological outcome.
This monograph is a research-use reference. It describes composition and the contexts in which the compound has been studied — it is not medical advice, a description of effects, or a recommendation for use. Sold strictly for laboratory and research use; not for human or animal consumption.