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The IGF-1 LR3 peptide is a modified analog of insulin-like growth factor 1 (IGF-1), engineered so that it engages the IGF-1 receptor while resisting the binding proteins that normally sequester native IGF-1. That single design change, a more available IGF-1 receptor ligand, is what makes it a distinct research tool at the effector end of the growth hormone axis.
This article describes the structure of IGF-1 LR3, the two modifications that define it, the receptor-binding and signaling research behind it, how it sits alongside the rest of the growth-axis catalog, and how the material is verified.
Research Snapshot
- IGF-1 LR3 (Long Arg3 IGF-1) is a synthetic 83-residue analog of human IGF-1. Its molecular formula is C400H625N111O115S9 and its molecular weight is approximately 9,117.53 g/mol.
- It carries two modifications from native IGF-1: an arginine substitution at position 3, and a 13-residue N-terminal extension. Together these alter its interaction profile with the IGF-binding proteins.
- The practical consequence studied in research is availability: by binding the IGF-binding proteins (IGFBPs) far more weakly, IGF-1 LR3 remains free to engage its receptor in experimental systems where native IGF-1 would be sequestered (Tomas et al., 1993).
- It is studied for IGF-1 receptor (IGF-1R) binding dynamics and downstream signaling pathway analysis under defined in vitro conditions, at the effector end of the growth hormone axis.
- Pure Health Peptides supplies IGF-1 LR3 as a lyophilized Vial, part of the wider catalog. Every lot is finished and tested in the US, routed through independent, ISO/IEC 17025-accredited testing by Ethos Analytics as the exclusive testing partner.
Introduction
Insulin-like growth factor 1 is the molecule at the bottom of the growth hormone axis, the effector that carries much of the signal initiated further upstream. It is also one of the most tightly regulated: in native form, IGF-1 spends most of its time bound to a family of IGF-binding proteins that control where and when it can reach its receptor. That regulation makes native IGF-1 an awkward research subject, because so little of it is free at any moment.
IGF-1 LR3 is the analog built to get around that. This article stays with the molecule and the preclinical research built on it: the structural modifications, the reduced binding-protein affinity that follows, the IGF-1 receptor signaling it is used to study, and the verification chain underneath the material.
It describes findings in preclinical and in vitro systems and holds to research-use framing throughout.
The IGF-1 LR3 Peptide: A Modified IGF-1 Analog
IGF-1 LR3 is native IGF-1 with two deliberate changes, and its name records both. “Arg3” refers to the arginine substituted in at position 3, replacing the glutamic acid found in native IGF-1. “Long” refers to the 13-residue extension added to the N-terminus. The result is an 83-residue peptide with a molecular weight of approximately 9,117.53 g/mol, considerably larger than native IGF-1’s 70 residues.
Neither modification changes the region of the molecule that engages the receptor. Instead, both target the interaction with the IGF-binding proteins. Because the receptor-binding surface is preserved while the binding-protein interaction is weakened, IGF-1 LR3 behaves as a receptor ligand that is far more available than the native molecule.
As a defined synthetic sequence, its identity is confirmed by mass spectrometry against its theoretical mass, the basis of lot-level verification.
Why the Modifications Matter: Binding-Protein Evasion
The reason researchers reach for IGF-1 LR3 rather than native IGF-1 comes down to the binding proteins. Native IGF-1 is bound with high affinity by the IGFBP family, which regulates its availability and dramatically shortens the window in which it can act in an experimental system. The Arg3 substitution and the N-terminal extension together reduce that binding-protein affinity, so a much larger fraction of the analog stays free (Tomas et al., 1993).
For a research setting, that translates to a more stable, more consistently available IGF-1 receptor ligand, which is exactly what is wanted when the goal is to study receptor binding or downstream signaling without the confounding variable of binding-protein sequestration.
The modifications do not create a new activity; they remove an obstacle to studying the existing one.
IGF-1 Receptor Binding and Signaling Research
With the availability problem solved, IGF-1 LR3 is used as a tool for the receptor itself. The IGF-1 receptor is a receptor tyrosine kinase, and its engagement initiates well-mapped intracellular signaling cascades. IGF-1 LR3 is studied for its binding to IGF-1R and for the downstream signaling pathway analysis that follows, under the defined in vitro conditions the literature describes (Rinderknecht & Humbel, 1978, established the native structure this analog is built from).
This places IGF-1 LR3 at the effector end of the growth hormone axis. Upstream, the axis is driven by GHRH analogs and secretagogues; IGF-1 is where much of that upstream signaling ultimately converges. Studying the analog therefore complements work on the upstream compounds, all strictly in preclinical and in vitro terms.
IGF-1 LR3 in the Growth-Axis Toolkit
IGF-1 LR3 is most useful understood in relation to the rest of the axis. Upstream sit the GHRH analog Tesamorelin, the combined CJC-1295 (DAC)/Ipamorelin, Sermorelin, and the secretagogue Hexarelin, which is covered in its own article.
Closest to IGF-1 LR3 mechanistically are the IGF-1 variants: MGF, the mechano growth factor splice variant of IGF-1, and its pegylated form PEG-MGF, both of which come from the same gene by different routes.
Held side by side, these give a research program the full arc of the axis: GHRH analogs and secretagogues at the top, IGF-1 and its variants at the effector end. Each is supplied as a lyophilized vial and each is a distinct receptor-level or ligand-level tool rather than a substitute for another.
Verification
Underneath the compound is the verification chain. Pure Health Peptides does not manufacture the material; production is sourced from qualified third-party manufacturers, and the material is finished and tested in the US.
Every lot is routed through independent, ISO/IEC 17025-accredited testing by Ethos Analytics as the exclusive testing partner, and each qualified lot’s Certificate of Analysis is published in the COA Library, in the vial section, retrievable by batch ID. For a lyophilized vialed peptide the appropriate panel extends beyond identity, purity, and quantity to include endotoxin and microbial limits, because contamination can enter downstream of synthesis through handling, lyophilization, vial filling, storage, and transit.
The Testing Process page documents how that verification runs, and the Manufacturing Process page covers where the material comes from. The guide to reading a Certificate of Analysis walks through the panel field by field.
Where IGF-1 LR3 Sits in Growth-Axis Research
For researchers studying IGF-1 signaling, IGF-1 LR3 is a specific and well-characterized tool: a modified analog that preserves the receptor-binding region while shedding most of the binding-protein regulation that complicates native IGF-1.
Its research value rests on that availability, a dependable IGF-1 receptor ligand for binding and signaling work, and on its position at the effector end of the growth hormone axis. As research on IGF-1R signaling continues, a stable, available IGF-1 analog remains a valuable reference compound, and IGF-1 LR3 holds a clear place at the base of the growth-axis cluster in the catalog.
Frequently Asked Questions
What is the IGF-1 LR3 peptide?
IGF-1 LR3 (Long Arg3 IGF-1) is a synthetic 83-residue analog of human insulin-like growth factor 1. Its molecular formula is C400H625N111O115S9 and its molecular weight is approximately 9,117.53 g/mol.
What do the “Long” and “Arg3” in the name mean?
“Arg3” is an arginine substituted at position 3 in place of native IGF-1’s glutamic acid; “Long” is a 13-residue extension added to the N-terminus. Both modifications reduce the analog’s binding to the IGF-binding proteins.
Why is IGF-1 LR3 used instead of native IGF-1 in research?
Native IGF-1 is largely sequestered by IGF-binding proteins, leaving little free to act. IGF-1 LR3 binds those proteins far more weakly, so more of it stays available to engage the IGF-1 receptor in experimental systems.
What is IGF-1 LR3 studied for?
IGF-1 receptor (IGF-1R) binding dynamics and downstream signaling pathway analysis, under defined in vitro conditions, at the effector end of the growth hormone axis.
What carrier format is IGF-1 LR3 available in, and how is it verified?
A lyophilized vial. Every lot is finished and tested in the US and routed through independent, ISO/IEC 17025-accredited testing by Ethos Analytics, with a lot-specific Certificate of Analysis published in the COA Library.
References
- Rinderknecht E, Humbel RE. The amino acid sequence of human insulin-like growth factor I and its structural homology with proinsulin. Journal of Biological Chemistry, 1978;253(8):2769-2776. https://doi.org/10.1016/S0021-9258(17)40889-1
- Tomas FM, et al. Insulin-like growth factor-I (IGF-I) and especially IGF-I variants are anabolic in dexamethasone-treated rats. Biochemical Journal, 1993;293(1):211-217. https://doi.org/10.1042/bj2930211
- Laviola L, Natalicchio A, Giorgino F. The IGF-I signaling pathway. Current Pharmaceutical Design, 2007;13(7):663-669. https://pubmed.ncbi.nlm.nih.gov/17346182/
- International Organization for Standardization / International Electrotechnical Commission. ISO/IEC 17025:2017, General requirements for the competence of testing and calibration laboratories. https://www.iso.org/standard/66912.html
