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What Is IGF-1 LR3? Long R3 IGF-1 Research Peptide Guide for UK Laboratory Research
What is IGF-1 LR3? IGF-1 LR3 — also referred to in the scientific literature as Long R3 IGF-I — is a synthetic 83-amino-acid polypeptide analogue of native human IGF-1, engineered specifically to overcome one practical limitation of the native hormone in laboratory research: its very short active half-life caused by rapid sequestration by IGF-binding proteins (IGFBPs). This page covers IGF-1 LR3 as a research compound in its own right — its structure, receptor mechanism, and downstream signalling — as a companion to, not a replacement for, the site’s existing dose-format research guide.
IGF-1 LR3 is supplied for in-vitro laboratory research only. It is not licensed by the MHRA as a medicinal product, and no dosing or administration guidance is provided in this guide or in any Ascend Peptides UK documentation. The compound is supplied for use by laboratories, academic institutions and research scientists for cell culture, receptor pharmacology and endocrine pathway research applications only.
Every batch of IGF-1 LR3 supplied by Ascend Peptides UK is HPLC verified at ≥98% purity by Janoshik laboratory, LC-MS confirmed for molecular identity, and accompanied by a publicly verifiable Certificate of Analysis.
What Is IGF-1 LR3 at the Molecular Level?
IGF-1 LR3 is a modified analogue of endogenous Insulin-like Growth Factor 1 (IGF-1), a 70-amino-acid polypeptide hormone structurally related to insulin. IGF-1 LR3 carries two specific structural modifications relative to native IGF-1: an arginine substitution for the glutamic acid normally present at position 3 of the native sequence (the source of the “R3” in its name), and a 13-amino-acid extension (sequence MFPAMPLLSLFVN) added at the N-terminus. Together these modifications extend the chain from 70 to 83 amino acids. The molecular identity is documented below.
|
Molecular Property |
Value |
|---|---|
|
Compound name |
IGF-1 LR3 / Long R3 IGF-I (Long Arg3 Insulin-like Growth Factor 1); not an INN-assigned compound |
|
Peptide class |
IGF-1 analogue; 83-amino-acid polypeptide/protein |
|
Structural modifications |
13-amino-acid N-terminal extension (MFPAMPLLSLFVN); Arg substitution for Glu at position 3 of the native IGF-I domain |
|
Length |
83 amino acid residues total (70-residue native IGF-I domain + 13-residue N-terminal extension) |
|
Approximate molecular mass |
~9.1 kDa. The exact mass differs slightly between the fully reduced chain and the correctly folded, disulfide-bonded form (see note below) — figures quoted without specifying which state they describe should be treated as approximate. |
|
Disulfide structure |
Three intramolecular disulfide bonds in the correctly folded molecule, consistent with native IGF-1’s disulfide architecture |
|
Receptor target |
IGF-1 receptor (IGF-1R) — receptor tyrosine kinase; residual affinity for the insulin receptor (IR) and IR/IGF-1R hybrid receptors |
|
Research category |
Growth Factor Research Peptide (IGF-1 axis, downstream of GH) |
|
Supplied format |
Lyophilised powder — white to off-white |
|
Third-party testing |
Janoshik — HPLC + LC-MS verified; endotoxin (LAL) assessment recommended for cell culture use |
Neither structural modification changes which receptor IGF-1 LR3 binds — it remains an IGF-1R-directed molecule. What they change is IGF-1 LR3’s interaction with the proteins that normally regulate native IGF-1’s bioavailability: the IGF-binding proteins (IGFBPs) and, to a lesser extent, the IGF-2R/mannose-6-phosphate clearance receptor. That distinction — same receptor target, altered regulatory-protein interaction — is the key structural fact to hold onto when comparing IGF-1 LR3 to native IGF-1.
The full molecular identity of IGF-1 LR3 is confirmed on every Ascend Peptides UK batch by independent LC-MS analysis through Janoshik laboratory, with the measured molecular weight matched against the expected mass (~9.1 kDa, accounting for the small difference between the reduced and disulfide-bonded forms noted above) to confirm structural identity. The complete laboratory quality control workflow is documented on the how we test peptides page.
IGF-1 LR3 and Native IGF-1: Why the Structural Differences Matter
Native IGF-1 has a very short active half-life in physiological and cell-culture environments — commonly reported in the low tens of minutes — because it is rapidly bound by IGF-binding proteins (IGFBPs), a family of carrier proteins that regulate IGF-1’s availability to its receptor. The two structural modifications in IGF-1 LR3 substantially reduce its affinity for IGFBPs, which is the principal reason IGF-1 LR3 remains bioactive in cell culture media for a much longer window than native IGF-1 without repeated media replenishment. IGF-1 LR3 also shows reduced affinity for the IGF-2R/mannose-6-phosphate receptor, a clearance pathway that further limits native IGF-1’s persistence.
This reduced-IGFBP-binding property is well documented in the peptide’s original characterisation literature (Francis et al., 1992) and in subsequent comparative work on IGF-1 variants with reduced IGFBP affinity (Tomas et al., 1995). Researchers should treat this as a specific, mechanistically explained pharmacokinetic difference — not a claim that IGF-1 LR3 is simply a “stronger” version of IGF-1. The two compounds engage the same receptor; what differs is how long each remains available to do so in an experimental system.
IGF-1 Receptor Signalling and Downstream Pathways
IGF-1 LR3 acts as an agonist at the IGF-1 receptor (IGF-1R), a receptor tyrosine kinase expressed across many tissue and cell-line types. In laboratory research models, receptor binding triggers receptor autophosphorylation and activates two principal downstream cascades: the PI3K/Akt pathway, associated with cell survival and metabolic signalling, and the MAPK/ERK pathway, associated with cell proliferation and differentiation. These two cascades are the standard reference framework for interpreting IGF-1R-driven experimental outcomes in the published literature (LeRoith et al., 1995).
An important pharmacological caveat for experimental design: IGF-1R belongs to the same receptor family as the insulin receptor (IR), and the two receptors can form IR/IGF-1R hybrid receptors. IGF-1 LR3 retains residual affinity for IR and IR/IGF-1R hybrids in addition to its primary IGF-1R target. Study designs that specifically require pathway isolation — for example, distinguishing IGF-1R signalling from insulin-receptor-mediated metabolic effects — should account for this cross-reactivity rather than treat IGF-1 LR3 as an absolutely pure IGF-1R probe.
For upstream context, the compounds that stimulate endogenous GH secretion — and therefore endogenous IGF-1 production — act through entirely different receptors. The Tesamorelin research guide covers GHRH-receptor signalling, and the Ipamorelin research guide covers GHSR-1a signalling. IGF-1 LR3 allows researchers to study the downstream growth-factor component of this axis directly, independent of upstream pituitary GH release.
IGF-1 LR3 Within the GH/IGF Research Axis
Research peptides acting on the growth hormone axis intervene at different points in the hypothalamic-pituitary-IGF cascade. GHRH analogues and GHRPs act upstream, at the pituitary, to stimulate GH secretion; GH then drives hepatic and local IGF-1 production. IGF-1 LR3 acts downstream of all of this, directly at the IGF-1 receptor, bypassing the need for upstream GH stimulation entirely. This makes it a mechanistically distinct research tool from every upstream GH-axis compound in the Ascend Peptides UK range.
Because IGF-1 LR3 activates IGF-1R directly, it is sometimes used alongside an upstream GHRH analogue or GHRP as an independent variable within a broader GH-axis research protocol, allowing the downstream and upstream components of the pathway to be studied in the same experimental design without one compound’s mechanism confounding the other’s. See the GH axis research peptides UK hub for the complete category framework across all five compounds in this range.
Binding-Protein Interaction and Receptor-Downregulation Considerations
Two research-design considerations follow directly from IGF-1 LR3’s structural profile. First, its reduced IGFBP affinity is what sustains receptor stimulation in culture without repeated compound addition — the primary practical reason it is used in place of native IGF-1 for longer-duration cell culture work. Second, that same sustained stimulation means multi-day assays should account for the possibility of dose-dependent IGF-1R downregulation as an experimental variable, since continuous receptor occupancy can itself alter receptor expression over time in some cell models.
Neither consideration is unique to Ascend Peptides UK material — both are properties of the IGF-1 LR3 molecule itself, documented in the peptide pharmacology literature, and are noted here so researchers can factor them into experimental design rather than treat IGF-1 LR3 as behaviourally identical to native IGF-1 at every timepoint.
Evidence Base and Research Limitations
Researchers designing experiments around IGF-1 LR3 should be aware of some specific limits to the current evidence base:
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The reduced-IGFBP-affinity property of IGF-1 LR3 is well established from the peptide’s original characterisation work (Francis et al., 1992) and subsequent comparative studies (Tomas et al., 1995), but published in-vitro data are concentrated in specific cell-line models (notably fibroblast and myoblast systems) and should not be assumed to generalise identically across every cell type without independent verification.
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The IGF-1R/insulin-receptor cross-reactivity noted above means that experimental outcomes attributed to “IGF-1R signalling” in a given assay may include a contribution from IR or hybrid-receptor engagement unless the experimental design specifically controls for it.
-
The PI3K/Akt and MAPK/ERK signalling framework referenced above (LeRoith et al., 1995) describes IGF-1R signalling broadly; compound-specific kinetic differences between native IGF-1 and IGF-1 LR3 at these downstream nodes are a narrower and less exhaustively characterised area of the literature than the receptor-binding and IGFBP-affinity work.
These limitations are a normal feature of an actively used research tool rather than a reason to dismiss IGF-1 LR3’s research relevance — they are simply the context a rigorous experimental design should account for.
Research-Grade Verification Standards for IGF-1 LR3
IGF-1 LR3 is a large, structurally complex 83-amino-acid polypeptide analogue (~9.1 kDa) frequently used in live cell culture systems, which makes analytical verification — including endotoxin testing — particularly important. Four documentation standards distinguish a verified UK supplier from an unverified one. The complete framework is set out on the batch verification page.
|
Documentation Standard |
Industry Norm |
Ascend Peptides UK |
|---|---|---|
|
HPLC purity verification |
Self-reported by the supplier |
Independent HPLC by Janoshik, ≥98% verified |
|
LC-MS molecular identity |
Often not performed |
LC-MS confirmation on every batch, confirming the 83-residue structure |
|
Endotoxin (LAL) awareness |
Rarely flagged for cell-culture-relevant peptides |
Endotoxin considerations documented for researchers running live cell assays |
|
Batch-specific Certificate of Analysis |
Generic or unavailable |
Per batch CoA tied to vial lot number |
For the complete research grade standards framework that defines what “research grade” actually means in UK laboratory peptide supply, see the research grade standards page.
Storage Note
IGF-1 LR3 follows the standard lyophilised-peptide storage protocol used across the Ascend Peptides UK catalogue. Full storage, reconstitution and handling detail — including solvent selection and aliquoting practice — is covered in depth in the peptide storage guide and the reconstitution guide, rather than repeated here.
IGF-1 LR3 Research Resources at Ascend Peptides UK
This page covers IGF-1 LR3 as a research compound — its structure, mechanism and signalling. For product specification, pricing and detailed cell-culture / reconstitution protocol guidance, see the dedicated resources below.
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IGF-1 LR3 1mg — the standalone product listing.
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IGF-1 LR3 1mg research guide — practical laboratory application and reconstitution reference.
IGF-1 LR3 is one compound within the wider GH axis research peptides UK range, itself part of the complete research peptides UK catalogue.
What Is IGF-1 LR3? Frequently Asked Questions
What is IGF-1 LR3?
IGF-1 LR3 (Long Arg3 Insulin-like Growth Factor 1, also called Long R3 IGF-I in the scientific literature) is a synthetic 83-amino-acid polypeptide analogue of native human IGF-1 (70 amino acids), carrying a 13-amino-acid N-terminal extension and an arginine substitution for glutamic acid at position 3 of the native IGF-I domain. In its correctly folded form it retains the three intramolecular disulfide bonds characteristic of native IGF-1. These modifications substantially reduce its affinity for IGF-binding proteins compared with native IGF-1, while leaving its IGF-1 receptor target unchanged.
Is IGF-1 LR3 more potent than native IGF-1?
IGF-1 LR3 is not more potent at the receptor level in the sense of activating IGF-1R differently — it binds the same receptor. What differs is bioavailability: its reduced IGF-binding-protein affinity means more of the compound remains free and available to engage IGF-1R over a given experimental timeframe, compared with native IGF-1, which is rapidly sequestered by IGFBPs.
Does IGF-1 LR3 only bind the IGF-1 receptor?
No. While IGF-1R is its primary target, IGF-1 LR3 retains residual affinity for the insulin receptor (IR) and IR/IGF-1R hybrid receptors. Experimental designs investigating metabolic or insulin-adjacent pathways should account for this rather than treat IGF-1 LR3 as an exclusively selective IGF-1R probe.
What downstream pathways does IGF-1 LR3 activate?
IGF-1 LR3 activates the same downstream cascades as native IGF-1 signalling through IGF-1R: the PI3K/Akt pathway, associated with cell survival and metabolic signalling, and the MAPK/ERK pathway, associated with cell proliferation and differentiation.
How does IGF-1 LR3 relate to Tesamorelin and Ipamorelin?
Tesamorelin and Ipamorelin act upstream, at the pituitary, to stimulate endogenous growth hormone (GH) secretion. IGF-1 LR3 acts downstream, directly at the IGF-1 receptor, independent of upstream GH release. The three compounds intervene at different points in the same GH/IGF research axis and are mechanistically distinct research tools.
What is the WADA status of IGF-1 LR3?
IGF-1 LR3, along with IGF-1 and its analogues, is listed on the World Anti-Doping Agency (WADA) Prohibited List under category S2 (Peptide Hormones, Growth Factors, Related Substances and Mimetics), prohibited at all times for athletes subject to WADA jurisdiction. Ascend Peptides UK supplies IGF-1 LR3 for in-vitro laboratory research only.
What is the MHRA status of IGF-1 LR3 in the UK?
IGF-1 LR3 supplied by Ascend Peptides UK is not licensed as a medicinal product under the UK Human Medicines Regulations 2012. It is supplied strictly for in-vitro laboratory research. The Medicines and Healthcare products Regulatory Agency (MHRA) is the relevant UK medicines regulator.
Scientific References
Francis, G.L., Ross, M., Ballard, F.J., Milner, S.J., Senn, C., McNeil, K.A., Wallace, J.C., King, R., & Wells, J.R. (1992). “Novel recombinant fusion protein analogues of insulin-like growth factor (IGF)-I indicate the relative importance of IGF-binding protein and receptor binding for enhanced biological potency.” Journal of Molecular Endocrinology, 8(3), 213–223. — the original characterisation of the Long R3 IGF-I structural modifications referenced in the molecular properties table above.
Tomas, F.M., Knowles, S.E., Owens, P.C., et al. (1995). “IGF-I variants that bind poorly to IGF-binding proteins show more potent biological activity than native IGF-I.” Journal of Endocrinology. — comparative work on the reduced-IGFBP-affinity property referenced above.
LeRoith, D., Werner, H., Beitner-Johnson, D., & Roberts, C.T. Jr. (1995). “Molecular and cellular aspects of the insulin-like growth factor I receptor.” Endocrine Reviews, 16(2), 143–163. — foundational review of IGF-1R structure and downstream signalling, including the PI3K/Akt and MAPK/ERK cascades referenced above.
RESEARCH USE ONLY
All products supplied by Ascend Peptides UK are intended strictly for in-vitro laboratory research purposes only. IGF-1 LR3 is not a licensed medicinal product under the UK Human Medicines Regulations 2012, and is not for human or veterinary use. No dosing or administration guidelines are provided. Purchasers must be 18 years of age or older and must confirm that products are being purchased solely for lawful laboratory research purposes. Ascend Peptides UK reserves the right to request additional information regarding intended research use and to decline orders where appropriate.
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