IGF-1 LR3 · Research brief

What Is IGF1 LR3 Same as IGF-1 LR3? (Peptide Clarified)

Real Peptides Research TeamEditorial

Updated April 10, 20268 min read

59 WORDS

Short answer

IGF1 LR3 and IGF-1 LR3 represent the same peptide molecule. The notation difference is stylistic, not chemical. Research suppliers, pharmaceutical databases, and clinical literature use both naming conventions interchangeably because there's no regulatory standard forcing consistency. The confusion multiplies when researchers encounter 'Long R3 IGF-I' in peer-reviewed journals, 'IGF-1 LR3' on supplier spec sheets, and 'IGF1-LR3' in patent filings.

Key takeaways

IGF1 LR3 and IGF-1 LR3 are identical molecules. The hyphen represents a stylistic choice in nomenclature, not a chemical distinction.
The CAS registry number 946870-92-4 unambiguously identifies both notations as the same 83-amino-acid synthetic analog with N-terminal extension and Glu3Arg substitution.
Molecular weight verification (9,117.5 Da) and sequence confirmation are the only reliable supplier quality checks. Product name alone is insufficient.
The structural modifications reduce IGFBP binding affinity by 100-fold and extend serum half-life from 10 minutes (native IGF-1) to 20–30 hours.
Researchers cross-referencing literature must search all notational variants (IGF1 LR3, IGF-1 LR3, Long R3-IGF-I, LR3-IGF-I) to capture the full body of published work on this peptide.

We've worked with hundreds of research teams ordering peptides for biological assays. The single most common question we field isn't about molecular weight or reconstitution protocols. It's whether IGF1 LR3 and IGF-1 LR3 are distinct compounds requiring separate control groups.

What is IGF1 LR3 and is it the same as IGF-1 LR3?

IGF1 LR3 and IGF-1 LR3 are identical. Both names refer to Long-Arg3-IGF-I, a synthetic peptide analog of human insulin-like growth factor with an N-terminal 13-amino-acid extension and an arginine substitution at position 3. This structural modification reduces IGF binding protein affinity by 100-fold and extends the biological half-life from 10 minutes (endogenous IGF-1) to approximately 20–30 hours. The nomenclature variance reflects stylistic preferences across chemical suppliers and research publications, not molecular difference.

The IGF1 LR3 molecule isn't a naturally occurring peptide. It was engineered in the 1980s to overcome the extremely short half-life of endogenous IGF-1, which circulates in serum bound almost entirely to IGFBPs. Binding proteins that sequester it and prevent receptor activation. The 'LR3' designation breaks down as: 'L' for 'Long' (the 13-amino-acid N-terminal extension), 'R' for arginine (replacing glutamic acid at position 3), and '3' marking that substitution site. When you see IGF1 LR3 versus IGF-1 LR3, you're looking at two notational conventions for the same chemical structure: one hyphenates the descriptor, one doesn't.

Why IGF1 LR3 and IGF-1 LR3 Generate Different Search Results

Supplier catalogues list the peptide inconsistently. One research supplier uses 'IGF-1 LR3' as the primary SKU name. Another lists it as 'IGF1-LR3' with a parenthetical '(Long R3 IGF-I)' descriptor. Academic literature references it as 'Long R3-IGF-I' in methods sections, then abbreviates to 'LR3-IGF-I' in results tables. Patent databases file it under 'insulin-like growth factor I, [Arg3]-', while regulatory submissions refer to it as 'Long-Arg3-human-IGF-I'. The notation split creates artificial SEO separation. Researchers searching 'IGF-1 LR3' might miss critical supplier spec sheets filed under 'IGF1 LR3', even though they reference the same CAS number.

The hyphen itself carries no chemical meaning. Standard biochemical nomenclature hyphenates descriptors from base molecule names. 'IGF-1' separates 'insulin-like growth factor' from the type designation '1'. Adding 'LR3' after that base name follows no universal convention. Some authors treat 'LR3' as a suffix requiring no separator, yielding 'IGF1 LR3'. Others treat it as an appended descriptor requiring a hyphen, yielding 'IGF-1 LR3'. Both are correct by informal precedent; neither is enforced by IUPAC or any regulatory authority.

The Structural Modification That Defines IGF1 LR3

Endogenous IGF-1 consists of 70 amino acids arranged in a three-domain structure stabilised by disulphide bonds. It circulates at nanomolar concentrations bound to six distinct IGF binding proteins (IGFBP-1 through IGFBP-6), which regulate its bioavailability and prevent inappropriate receptor activation. When IGF-1 binds to the IGF-1 receptor (IGF1R) on cell surfaces, it triggers the PI3K/Akt and MAPK/ERK signalling cascades. Pathways that promote cell proliferation, differentiation, and survival. The problem in research settings: unbound IGF-1 has a serum half-life of 10–12 minutes, making sustained receptor activation nearly impossible without continuous infusion.

IGF1 LR3 addresses this through two structural changes. First, the N-terminal extension adds 13 amino acids (Met-Phe-Pro-Ala-Met-Pro-Leu-Ser-Ser-Leu-Phe-Val-Asn) before the native IGF-1 sequence, increasing molecular weight from 7.6 kDa to approximately 9.1 kDa. Second, the Glu3Arg substitution replaces glutamic acid at position 3 with arginine. These modifications reduce IGFBP binding affinity by 100- to 1000-fold depending on which binding protein is measured, while maintaining near-full affinity for IGF1R. The result: a peptide that circulates unbound far longer and activates receptors with 2–3 times the potency of native IGF-1 in cell-based assays.

Our team has seen researchers mistakenly believe that 'IGF1 LR3' represents a 'fast-acting' variant while 'IGF-1 LR3' is 'extended-release'. That's incorrect. The identical molecule produces identical receptor kinetics. What changes is systemic clearance rate, not cellular mechanism. A myoblast exposed to 10 nM IGF1 LR3 shows the same phosphorylated Akt curve whether you ordered the vial labelled 'IGF-1 LR3' or 'IGF1 LR3'.

IGF1 LR3 Same as IGF-1 LR3: Supplier Verification Criteria

The naming inconsistency creates quality control challenges. When evaluating supplier spec sheets, researchers should verify identity through molecular weight, not product name. IGF1 LR3 (by either notation) has a theoretical molecular weight of 9,117.5 Da. Mass spectrometry certificates of analysis should report [M+H]+ peaks within ±1 Da of this value. HPLC purity should exceed 98%, with the dominant peak eluting at the retention time corresponding to an 83-amino-acid sequence. If the supplier lists molecular weight as 7,649 Da, they're shipping native IGF-1, not the Long R3 analog. Regardless of what the product label says.

Second verification: sequence confirmation. Reputable suppliers provide full amino acid sequence on their spec sheets. IGF1 LR3 must begin with the 13-amino-acid extension (MFPAMPLLSLFVN) followed by the native IGF-1 sequence starting at position 14. Position 3 of the native sequence (position 16 of the extended molecule) must be arginine, not glutamic acid. A supplier listing 'IGF-1 LR3' but providing a certificate referencing 70 amino acids has mislabelled their product.

Our experience: researchers waste more time cross-referencing supplier catalogues than they do designing experiments. The peptide industry has no incentive to standardise naming because regulatory oversight is limited to manufacturing compliance, not nomenclature. We maintain internal SKU mapping that cross-references every known notation to a single CAS registry number (946870-92-4 for IGF1 LR3) to prevent duplicate orders.

IGF1 LR3 Same as IGF-1 LR3: Comparison Across Notations

Notation Variant	Molecular Weight (Da)	Amino Acid Count	IGFBP-3 Binding Affinity (vs Native IGF-1)	Half-Life (Serum)	Registry Identifier
IGF1 LR3	9,117.5	83	100-fold reduced	20–30 hours	CAS 946870-92-4
IGF-1 LR3	9,117.5	83	100-fold reduced	20–30 hours	CAS 946870-92-4
Long R3-IGF-I	9,117.5	83	100-fold reduced	20–30 hours	CAS 946870-92-4
LR3-IGF-I	9,117.5	83	100-fold reduced	20–30 hours	CAS 946870-92-4
Native IGF-1 (comparison)	7,649	70	Baseline	10–12 minutes	CAS 67763-96-6

What If: IGF1 LR3 Scenarios

What If a Supplier Lists Both 'IGF1 LR3' and 'IGF-1 LR3' as Separate Products?

Request certificates of analysis for both SKUs and compare molecular weight, amino acid sequence, and HPLC retention time. If all three parameters match, the supplier has duplicate listings for inventory management reasons. Not because the compounds differ. Order whichever SKU has the lower per-milligram cost or faster shipping. If molecular weights diverge, one product is mislabelled or the supplier is conflating native IGF-1 with the Long R3 analog.

What If the Certificate Lists 'IGF-1' But the Product Name Includes 'LR3'?

Verify the amino acid count on the spec sheet. Native IGF-1 contains 70 amino acids; IGF1 LR3 contains 83. If the certificate lists 70 amino acids or a molecular weight near 7,649 Da, the supplier shipped native IGF-1 regardless of the label. Contact the supplier immediately. This represents a critical identity mismatch that invalidates any experimental results obtained using the product.

What If Published Research References 'Des(1-3)IGF-1' Instead of IGF1 LR3?

Des(1-3)IGF-1 is a different analog. It's native IGF-1 with the first three N-terminal amino acids removed, yielding a 67-amino-acid peptide with reduced IGFBP binding but no half-life extension. It is not the same molecule as IGF1 LR3. Researchers citing 'Des(1-3)IGF-1' are referencing a truncated variant, not the extended Long R3 form. Cross-referencing literature requires distinguishing between Des(1-3)IGF-1 (CAS 99652-23-2) and IGF1 LR3 (CAS 946870-92-4).

The Blunt Truth About IGF1 LR3 Nomenclature

Here's the honest answer: the peptide research community has had three decades to standardise this nomenclature and hasn't. The inconsistency isn't an oversight. It's the result of fragmented supplier ecosystems, uncoordinated academic publishing conventions, and zero regulatory incentive to enforce naming uniformity for research-grade compounds. You will encounter 'IGF1 LR3', 'IGF-1 LR3', 'Long R3-IGF-I', 'LR3-IGF-I', and '[Arg3]-IGF-I' in the same literature review, all referencing CAS 946870-92-4. Treat the CAS number as the single source of truth. Product names are marketing; chemical registry identifiers are definitive.

The most common error we see isn't confusion between IGF1 LR3 and IGF-1 LR3. It's researchers ordering native IGF-1 thinking they bought the Long R3 analog because the supplier used ambiguous shorthand like 'recombinant human IGF-1' without specifying sequence length. If the spec sheet doesn't explicitly state '83 amino acids' or 'Long R3 analog', assume you're getting native IGF-1 until proven otherwise.

Our team sources peptides for protocols requiring precise molecular identity. We've rejected supplier shipments where the certificate molecular weight matched the expected value but amino acid sequencing revealed the wrong positional substitution. A quality control failure that product name alone would never catch. The lesson: verify through structure, not label. Explore high-purity research peptides where every batch includes full mass spectrometry and sequencing verification.

The notation IGF1 LR3 versus IGF-1 LR3 matters only to search engines and catalogue databases. Not to the receptor binding kinetics, signalling cascade activation, or experimental reproducibility that define research utility. Spend less time reconciling nomenclature and more time verifying the molecular identity of what arrives in the vial.

References

Peer-reviewed sources on IGF-1 LR3 indexed in PubMed, listed for research context. Real Peptides supplies IGF-1 LR3 for laboratory research use only.

IGF-1 LR3 does not promote growth in late-gestation growth-restricted fetal sheep. American journal of physiology. Endocrinology and metabolism, 2025. PMID 39679943. doi:10.1152/ajpendo.00259.2024
Intranasal long R3 insulin-like growth factor-1 treatment promotes amyloid plaque remodeling in cerebral cortex but fails to preserve cognitive function in male 5XFAD mice. Journal of Alzheimer's disease : JAD, 2025. PMID 39610283. doi:10.1177/13872877241299056
Recombinant expression of IGF-1 and LR3 IGF-1 fused with xylanase in Pichia pastoris. Applied microbiology and biotechnology, 2023. PMID 37261455. doi:10.1007/s00253-023-12606-0
Attenuated glucose-stimulated insulin secretion during an acute IGF-1 LR3 infusion into fetal sheep does not persist in isolated islets. Journal of developmental origins of health and disease, 2023. PMID 37114757. doi:10.1017/S2040174423000090
Long R3 insulin-like growth factor-I (IGF-I) infusion stimulates organ growth but reduces plasma IGF-I, IGF-II and IGF binding protein concentrations in the guinea pig. The Journal of endocrinology, 1995. PMID 7561636. doi:10.1677/joe.0.1460247

Questions

IGF1 LR3 and IGF-1 LR3 are the same peptide — both names refer to the 83-amino-acid Long-Arg3-IGF-I analog with an N-terminal extension and glutamic acid-to-arginine substitution at position 3. The hyphen in ‘IGF-1 LR3’ reflects stylistic preference in nomenclature, not chemical distinction. Both notations share the CAS registry number 946870-92-4, molecular weight of 9,117.5 Da, and identical amino acid sequence. Researchers using either name are referencing the same molecule.

Request the certificate of analysis and verify three parameters: molecular weight should be 9,117.5 Da (±1 Da by mass spectrometry), amino acid count must be 83 (not 70), and HPLC purity should exceed 98%. The amino acid sequence must begin with the 13-residue N-terminal extension (MFPAMPLLSLFVN) and show arginine at position 3 of the native IGF-1 portion. If the certificate lists molecular weight near 7,649 Da or 70 amino acids, the supplier has shipped native IGF-1 regardless of product labelling.

IGF1 LR3 exhibits 100- to 1000-fold reduced binding affinity for IGF binding proteins compared to native IGF-1, allowing it to circulate unbound and activate IGF-1 receptors with 2–3 times the potency in cell-based proliferation assays. The serum half-life extends from 10–12 minutes (native IGF-1) to 20–30 hours (IGF1 LR3) due to reduced IGFBP sequestration. Receptor binding affinity and downstream signalling through PI3K/Akt and MAPK/ERK pathways remain nearly identical — the key difference is systemic bioavailability, not cellular mechanism.

Academic journals, supplier catalogues, and patent databases follow no universal nomenclature standard for modified peptides. The same molecule appears as ‘IGF1 LR3’, ‘IGF-1 LR3’, ‘Long R3-IGF-I’, ‘LR3-IGF-I’, and ‘[Arg3]-IGF-I’ depending on author preference and publication style guidelines. Regulatory bodies like IUPAC have not enforced naming conventions for research-grade synthetic peptides, so notation remains inconsistent across literature. Researchers conducting systematic reviews must search all variants to capture the full body of published work.

Yes, if both products are verified as authentic Long R3 analogs through molecular weight and sequence confirmation. The nomenclature difference carries no experimental consequence — receptor binding kinetics, signalling activation, and dose-response curves are identical because the molecular structure is identical. However, switching suppliers requires revalidation of purity, reconstitution protocols, and storage stability even when the notation remains the same, as manufacturing processes vary more significantly than nomenclature.

Des(1-3)IGF-1 is a different peptide analog — it’s native IGF-1 with the first three N-terminal amino acids removed, yielding a 67-amino-acid structure with reduced IGFBP binding but no half-life extension. It is not equivalent to IGF1 LR3. Des(1-3)IGF-1 carries CAS number 99652-23-2, whereas IGF1 LR3 is CAS 946870-92-4. Researchers citing ‘Des(1-3)IGF-1’ in literature are referencing a truncated variant, not the extended Long R3 form with the 13-amino-acid N-terminal addition.

Lyophilised IGF1 LR3 powder should be stored at −20°C in a desiccated environment before reconstitution. Once reconstituted with bacteriostatic water or sterile saline, store aliquots at −20°C to −80°C for long-term use (up to 6 months) or at 2–8°C for short-term use (up to 4 weeks). Avoid repeated freeze-thaw cycles, which denature the peptide structure and reduce receptor binding affinity. Stability data from synthesis facilities indicate that reconstituted IGF1 LR3 loses less than 5% activity over 30 days at 4°C, but degradation accelerates above 8°C.

Concentrations range from 1 nM to 100 nM depending on cell type and experimental endpoint. Myoblast proliferation assays commonly use 10–50 nM IGF1 LR3, while receptor phosphorylation studies may use lower concentrations (1–10 nM) to avoid receptor saturation. Dose-response curves should be established for each cell line, as sensitivity varies based on endogenous IGF-1 receptor density and IGFBP expression. Concentrations above 100 nM often produce maximal receptor activation with no additional effect, making them inefficient for mechanistic studies.

No. IGF1 LR3 is not FDA-approved for human use and is sold exclusively as a research reagent for in vitro and animal studies. Mecasermin (recombinant human IGF-1) is the only FDA-approved IGF-1-based therapy, indicated for severe primary IGF-1 deficiency in paediatric patients. IGF1 LR3 does not appear in any clinical trial databases for human administration and is prohibited in competitive sports by the World Anti-Doping Agency (WADA). Use is restricted to laboratory research under appropriate institutional biosafety protocols.

Reconstitute IGF1 LR3 in slightly acidic to neutral buffers (pH 5.0–7.4) to minimise aggregation and maintain solubility. Sterile water, bacteriostatic water, or phosphate-buffered saline (PBS) at pH 7.4 are standard solvents. Avoid highly alkaline conditions (pH >8.0), which promote peptide bond hydrolysis and disulphide bond rearrangement. Some protocols add 0.1% bovine serum albumin (BSA) to reconstitution buffer to reduce surface adsorption losses in storage vials, though this may interfere with downstream assays requiring serum-free conditions.

RESEARCH USE ONLY · NOT EVALUATED BY THE FDA