What is IGF-1 LR3?
IGF-1 LR3 is a synthetic 83-amino acid analog of human insulin-like growth factor 1 (IGF-1), engineered to carry two specific structural modifications that alter its interaction profile with binding proteins and receptor kinetics relative to the native hormone. It is catalogued under CAS number 946870-92-4 with a molecular formula of C₄₀₀H₆₂₅N₁₁₁O₁₁₅S₉ and a molecular weight of approximately 9117.5 g/mol. The compound is supplied as a lyophilized powder for laboratory research and is intended solely for research purposes, not for human use.
Within growth factor receptor biology, IGF-1 LR3 is studied primarily for two properties that distinguish it from native IGF-1: a substantially reduced affinity for the IGF-binding protein (IGFBP) family, and an extended circulating half-life in research model systems relative to the endogenous peptide. These properties make it a valuable mechanistic tool for isolating IGF-1 receptor (IGF-1R) signaling from the regulatory interference imposed by binding proteins in physiological settings.
Research programs using IGF-1 LR3 span IGF-1 receptor pharmacology, PI3K/Akt/mTOR pathway analysis, metabolic signaling in cell culture models, and structure-activity relationship studies of the IGF/insulin superfamily. It is catalogued separately from native IGF-1 because its binding protein resistance and modified pharmacokinetic profile make it a distinct experimental tool, not merely a more potent copy of the endogenous ligand.
What is the molecular architecture of IGF-1 LR3?
IGF-1 LR3 has a molecular weight of approximately 9117.5 g/mol and derives its structure from two deliberate modifications to the native 70-amino acid IGF-1 sequence.
The first modification is an arginine substitution at position 3. Native IGF-1 carries a glutamate at the third residue of the mature peptide. In LR3, this glutamate is replaced with an arginine—the "R3" in the compound name refers to this Arg3 substitution. This single residue change is the primary structural determinant of the dramatically reduced IGFBP binding affinity that characterizes the analog. The glutamate at position 3 in native IGF-1 contributes meaningfully to contacts with IGFBPs, particularly IGFBP-3; replacing it with arginine disrupts those electrostatic contacts and sharply reduces binding protein affinity without proportionately affecting IGF-1R engagement.
The second modification is a 13-amino acid N-terminal extension preceding the native IGF-1 sequence. This extension—the "Long R3" prefix—is a synthetic peptide leader that further attenuates binding protein affinity and is the structural feature responsible for extending the compound's effective half-life in research model systems. The extension does not appear to be required for IGF-1R activation; rather, it contributes to the IGFBP resistance phenotype in combination with the Arg3 substitution.
Together, these two modifications produce an 83-amino acid sequence (13-aa extension + 70-aa modified IGF-1 core) that retains high-affinity IGF-1R engagement while largely escaping the binding protein reservoir that sequesters native IGF-1 in vivo. The research-grade material is supplied as a lyophilized white powder stored at −20°C.
What is the IGF-1 receptor and why is it a research target?
The insulin-like growth factor 1 receptor (IGF-1R) is a receptor tyrosine kinase (RTK) belonging to the insulin receptor superfamily. It is a heterotetrameric transmembrane glycoprotein composed of two extracellular alpha subunits and two transmembrane beta subunits linked by disulfide bonds. The extracellular alpha subunits contain the ligand-binding domain, while the intracellular beta subunit portions carry the tyrosine kinase catalytic domains responsible for downstream signal propagation.
Ligand binding to the alpha subunits induces conformational rearrangement that activates the beta subunit kinase domains, triggering autophosphorylation at multiple tyrosine residues. These phosphorylated sites serve as docking platforms for intracellular adapter proteins including insulin receptor substrate-1 (IRS-1) and IRS-2, as well as the Shc adapter family. Recruitment and phosphorylation of these adapters initiates branching downstream signaling through two primary pathways: the PI3K/Akt axis and the Ras/MAPK/ERK axis.
IGF-1R is expressed broadly across tissue types and is studied in the context of cell proliferation signaling, survival pathway activation, metabolic regulation, and the crosstalk between growth factor and insulin signaling networks. Its homology with the insulin receptor—the two share approximately 70% amino acid identity in their kinase domains—makes it relevant to research programs examining metabolic signaling specificity, particularly the question of how structurally similar receptors transduce signals toward distinct cellular outcomes. IGF-1 LR3 is used in this context as a probe that can drive sustained IGF-1R activation without the dampening effect of IGFBP sequestration.
How do IGFBPs regulate IGF-1 bioavailability in research models?
The insulin-like growth factor binding protein (IGFBP) family comprises six structurally related proteins (IGFBP-1 through IGFBP-6) that bind IGF-1 and IGF-2 with affinities equal to or exceeding that of the IGF-1 receptor itself. In circulating plasma, the majority of IGF-1 is bound in a ternary complex with IGFBP-3 and an acid-labile subunit (ALS), which dramatically extends the half-life of the hormone but also limits its free bioavailability for receptor engagement.
This binding protein system introduces a major experimental variable in IGF-1 receptor research. When native IGF-1 is introduced to cell culture systems containing serum—or to in vivo models—the actual free concentration available for IGF-1R engagement is a function of both the added peptide concentration and the competing IGFBP concentrations in the experimental system. This makes precise dose-response characterization of IGF-1R signaling difficult with native IGF-1, because the binding protein buffer suppresses free ligand availability in a concentration- and time-dependent manner.
IGF-1 LR3 addresses this confound directly. Its sharply reduced IGFBP affinity—driven by the Arg3 substitution and N-terminal extension—means that a much larger fraction of added compound remains free and available for receptor engagement, even in serum-containing media. Published receptor signaling research has used this property to generate cleaner concentration-response relationships at IGF-1R and to examine downstream pathway activation at defined receptor occupancy levels that are difficult to achieve with the native ligand. AminoZone makes no therapeutic or outcome claims regarding IGF-1 LR3; it is studied for its receptor pharmacology and binding protein interaction properties in research settings.
What downstream signaling pathways does IGF-1R activation engage?
IGF-1R activation by IGF-1 LR3 in research models initiates two primary intracellular signaling axes that are extensively studied in growth factor and metabolic research programs.
The PI3K/Akt/mTOR axis. Following IGF-1R autophosphorylation and IRS-1/IRS-2 docking, phosphoinositide 3-kinase (PI3K) is recruited and activated. PI3K phosphorylates phosphatidylinositol 4,5-bisphosphate (PIP2) to generate phosphatidylinositol 3,4,5-trisphosphate (PIP3), which recruits Akt (protein kinase B) to the plasma membrane via its pleckstrin homology domain. Membrane-localized Akt is phosphorylated at Thr308 by PDK1 and at Ser473 by the mTORC2 complex, producing fully active Akt. Active Akt phosphorylates numerous downstream substrates including TSC2 (tuberous sclerosis complex 2), which releases mTORC1 from suppression, and FOXO transcription factors, which are excluded from the nucleus upon phosphorylation. mTORC1 activation drives downstream phosphorylation of S6K1 and 4E-BP1, key regulators of translational machinery activity. This axis is among the most extensively studied in both metabolic signaling research and cell biology broadly.
The Ras/MAPK/ERK axis. Shc adapter protein recruitment to phosphorylated IGF-1R leads to Grb2/SOS complex assembly and subsequent Ras GTPase activation. Active Ras drives the sequential kinase cascade through Raf → MEK1/2 → ERK1/2, with phosphorylated ERK translocating to the nucleus to modulate transcription factor activity. This pathway is studied in the context of mitogenic signaling, cell cycle entry, and the proliferative responses downstream of growth factor receptor activation.
In research models, the two pathways exhibit distinct kinetics and concentration-response profiles at IGF-1R. The PI3K/Akt arm is generally considered the primary metabolic output of IGF-1R activation, while the MAPK arm is more associated with proliferative signaling. IGF-1 LR3, by maintaining sustained free ligand availability, is used to study the temporal dynamics and crosstalk between these axes under conditions of prolonged receptor engagement that are difficult to model with rapidly sequestered native IGF-1.
How does IGF-1 LR3 compare to native IGF-1 as a research tool?
Native IGF-1 is the endogenous reference ligand for the IGF-1 receptor system and the structural parent of IGF-1 LR3. The two differ in chain length, N-terminal sequence, residue 3 identity, and IGFBP binding affinity—all of which have consequences for how they are deployed in research.
| Property | Native IGF-1 | IGF-1 LR3 |
|---|---|---|
| Amino acid length | 70 residues | 83 residues (13-aa extension + 70-aa modified core) |
| Position 3 residue | Glutamate (Glu3) | Arginine (Arg3) |
| N-terminal extension | None | 13-amino acid synthetic leader |
| IGFBP binding affinity | High (comparable to IGF-1R) | Markedly reduced |
| IGF-1R affinity | High | High (retained) |
| Half-life in research models | Short — rapidly sequestered by IGFBPs | Extended — reduced binding protein capture |
| Research application | Endogenous reference ligand | Binding-protein-resistant probe for IGF-1R signaling |
The extended half-life of IGF-1 LR3 in research settings has been quantified in comparative studies as substantially longer than that of native IGF-1 under equivalent experimental conditions. Published structural analyses of the IGFBP interaction surface attribute the majority of this effect to the Arg3 substitution, with the N-terminal extension contributing additional binding protein resistance through steric and electrostatic mechanisms at the N-terminal IGFBP contact region.
For research designs where the goal is characterizing IGF-1R signal transduction independently of binding protein regulatory effects, IGF-1 LR3 is the standard analog tool in the published growth factor literature.
What experimental contexts use IGF-1 LR3 as a research tool?
IGF-1 LR3 appears across several distinct research program types, each leveraging its binding protein resistance and sustained receptor engagement for different experimental objectives.
Receptor signaling kinetics studies. Because free ligand availability is controlled more precisely with IGF-1 LR3 than with native IGF-1 in serum-containing systems, it is used in time-course experiments characterizing the kinetics of PI3K/Akt and MAPK activation following defined IGF-1R stimulation. These studies benefit from the reduced IGFBP interference, which makes receptor occupancy a more predictable function of added compound concentration.
Crosstalk studies with the insulin receptor. Given the structural and signaling homology between IGF-1R and the insulin receptor (IR), research programs examining the specificity of downstream signal routing between the two receptors use IGF-1 LR3 as a selective IGF-1R activator. Its reduced IGFBP binding does not affect its receptor subtype preference—it remains an IGF-1R agonist—making it useful for dissecting pathway contributions in cells co-expressing both receptors.
mTOR pathway research. The PI3K/Akt/mTOR axis is a core subject of study across metabolic biology and cell physiology. IGF-1 LR3 is one of the standard exogenous growth factor stimuli used to activate this pathway in cell culture models, particularly in studies examining mTORC1 and mTORC2 complex outputs, S6K1/4E-BP1 phosphorylation dynamics, and crosstalk with nutrient sensing pathways.
Cell culture serum-free model systems. Serum-free or low-serum research culture systems reduce IGFBP content, which partially mitigates the binding protein confound even with native IGF-1. IGF-1 LR3 is nonetheless preferred in these contexts because residual binding proteins from serum supplements or endogenous secretion by cultured cells can still sequester native IGF-1 at levels that complicate quantitative receptor signaling studies.
What handling and storage requirements apply to IGF-1 LR3?
IGF-1 LR3 is supplied as a lyophilized powder and stored at −20°C to maintain structural integrity. As a large, disulfide-bonded 83-amino acid peptide, it is more susceptible to degradation than small synthetic peptides, and its structural integrity is directly relevant to receptor binding activity. Disulfide bond oxidation state, peptide backbone hydrolysis, and aggregation are the primary stability concerns under suboptimal storage conditions.
Research handling practices supporting reproducibility include maintaining consistent cold storage, limiting freeze-thaw cycles, protecting the lyophilized material from moisture, and avoiding prolonged exposure to room temperature during handling. Cold-chain transit conditions are relevant because thermal excursion during shipping can compromise the purity specification established at synthesis before the material reaches the researcher.
This article does not provide reconstitution or preparation instructions. Handling and preparation protocols are determined by the researcher according to their experimental requirements and applicable regulations.
How does AminoZone supply IGF-1 LR3?
AminoZone supplies IGF-1 LR3 as a research-grade compound held to a minimum purity specification of 98.0% by HPLC, with mass spectrometry identity confirmation verifying the correct molecular weight and sequence identity. Every order ships with a batch-specific Certificate of Analysis, and all shipments are cold-chain packaged as standard to protect the lyophilized material in transit.
For context on what HPLC purity and mass spectrometry confirmation quantify in practice—and why batch-specific documentation matters for reproducibility in growth factor receptor research—see the overview of research peptide purity standards. Specifications, available sizes, and pricing for IGF-1 LR3 are detailed on the IGF-1 LR3 product page. The full AminoZone research compound catalog, including related peptides studied in receptor signaling and growth factor biology, is available at all compounds. All material is intended for laboratory research use only. Not for human use.
This compound is a research chemical intended for laboratory and scientific research purposes only. It is not a drug, supplement, or food product, and is not intended to diagnose, treat, cure, or prevent any disease. AminoZone does not sell products for human consumption. Researchers are responsible for compliance with all applicable local, state, and federal regulations governing the purchase and use of research materials.