FREE SHIPPING ON ORDERS $250+
Precise Pep LabsPrecision in Every Vial
Compound Guides

IGF-1 LR3: Structure, Binding-Protein Affinity and the Research Record

IGF-1 LR3, or Long-[Arg3]-IGF-I, is a recombinant analogue of insulin-like growth factor-I with a 13-amino-acid N-terminal extension and arginine in place of glutamate at position 3. NMR work shows the folded core is essentially that of IGF-I, with the differences at the N-terminus, where IGF-binding proteins make contact. Its greater potency is not intrinsic: without binding proteins present it has been reported as less potent than native IGF-I. This guide covers the structure, the binding-protein and receptor evidence, laboratory uses, and our certificate for lot PPL-IG1-1.

Precise Pep Labs Research Editorial Team · November 7, 2026 · 14 min read

Key facts

  • IGF-1 LR3 (Long-[Arg3]-IGF-I) is native IGF-I with glutamate 3 replaced by arginine and a 13-residue N-terminal extension added, so the chain is 83 residues against the natural 70.
  • NMR studies found the IGF-I domain almost unchanged; the major structural difference is at the N-terminus, which the authors linked to the analogue's lower binding-protein affinity.
  • Its potency advantage depends on the system: in cell lines secreting IGF-binding proteins the human Long [Arg3] analogue outperformed IGF-I, but in chicken embryo fibroblasts, reported to secrete none detectably, the same analogue was less potent than IGF-I.
  • Reported type-1 receptor binding is slightly to about three-fold weaker than that of IGF-I, so the analogue trades receptor affinity for escape from binding proteins.
  • Our current lot PPL-IG1-1 was reported at 99.780 % batch average purity and 1.04 mg mean net content; the identity row names LC-MS but prints no observed molecular mass, and the endotoxin row prints PASS with no numerical result or method.
Research use only. This article is reference material for laboratory research. It does not describe or recommend any human or veterinary use, dosing or administration, and nothing here is medical advice. Precise Pep Labs materials are sold for in vitro research only.

What IGF-1 LR3 is

IGF-1 LR3 is a laboratory-made analogue of human insulin-like growth factor-I. Its full name in the literature is Long-[Arg3]-IGF-I, usually written Long R3 IGF-I or LR3 IGF-I, and it differs from the natural protein in two defined ways: the glutamate at position 3 is replaced by arginine, and a 13-amino-acid extension is attached to the N-terminus [2][3].

It was not discovered in tissue. It was designed and expressed in bacteria by a group at the CSIRO Division of Human Nutrition in Adelaide, as one of a family of recombinant IGF-I variants built to answer a specific experimental question: how much of IGF-I's activity in a culture dish is controlled by the binding proteins that surround it, rather than by the receptor it acts on [2][5]. That origin explains most of what follows: this is a research reagent whose defining property is a deliberately weakened interaction with one set of proteins.

The Precise Pep Labs IGF1-LR3 1mg vial is sold for in vitro research use only. Nothing in this article describes or recommends use in people or animals, and no part of it should be read as a protocol.

How IGF-1 LR3 differs from native IGF-1

Native human IGF-I is a single chain of 70 amino acids held together by three disulfide bridges, with a calculated molecular weight of 7,649. Its sequence is homologous to proinsulin across much of its length [1]. Two regions matter for this article: the first three residues of the chain, Gly-Pro-Glu, and the N-terminus generally, because that is where the binding proteins make contact.

The 13-residue N-terminal extension

The extension on LR3 came from a production problem rather than a biological design. Francis and colleagues expressed IGF-I in Escherichia coli as a fusion peptide carrying the first 11 amino acids of methionyl porcine growth hormone plus a Val-Asn dipeptide, 13 residues in total, ahead of the IGF-I sequence. They reported that the hydrophobic extension helped the molecule fold correctly and gave much higher yields of active product than refolding normal-length IGF-I had done [2]. The extension was kept rather than cleaved, so the finished analogue is 83 residues long: 13 added to the natural 70.

The Arg3 substitution

In the same work the glutamate at position 3 of the IGF-I sequence was replaced, in separate constructs, by glycine or arginine, giving Long [Gly3]-IGF-I and Long [Arg3]-IGF-I [2]. Position 3 was not chosen at random. The naturally occurring truncated form des(1-3)IGF-I, which lacks Gly-Pro-Glu entirely, had already been shown to be markedly more potent than IGF-I in cultured cells, and that gain was attributed to the loss of the glutamate at position 3 and the much weaker binding-protein interaction that followed [6][7]. Substituting arginine at the same position reproduces the effect without truncating the chain.

The three molecules side by side

Native IGF-Ides(1-3)IGF-IIGF-1 LR3 (Long-[Arg3]-IGF-I)
Chain length70 residues [1]67 residues; Gly-Pro-Glu removed from the N-terminus [6]83 residues; 13-residue extension added, Glu3 replaced by Arg [2][3]
OriginIsolated from serum; also made recombinantly [1]Found in bovine colostrum, human brain and porcine uterus, probably from post-translational cleavage; also synthesised [6]Recombinant only; expressed as a fusion peptide [2][5]
Residue 3GlutamateAbsentArginine
Reported IGFBP interactionNormalMuch reduced [6]Reduced; binds very poorly to bovine IGFBP-2 [5]
Reported type-1 receptor bindingReferenceNot increased relative to IGF-I [7]Slightly to around three-fold weaker than IGF-I in the systems tested [5][9]

The pattern in the last two rows is the single most important thing to understand about this molecule, and it is covered next.

What the binding proteins do

Insulin-like growth factors in a culture dish, or in an animal, are rarely free. Six IGF-binding proteins bind them with high affinity, and they do more than carry cargo: by holding IGFs away from the type-1 IGF receptor they can suppress mitogenesis, differentiation and survival signalling, while association with cell-surface or matrix components can instead concentrate an IGF near its receptor. Several binding proteins also have receptor-independent actions of their own [8].

Many cultured cell lines secrete binding proteins into their own medium, and when they do, a fraction of any IGF-I added is sequestered. An analogue that binds those proteins poorly escapes that sequestration, so more of it reaches the receptor. That, and not a stronger receptor interaction, is the mechanism the original authors proposed: King and colleagues found that [Gly3]- and [Arg3]-IGF-I bound very poorly to bovine IGFBP-2 and slightly less well than IGF-I to the type-1 receptor on rat L6 myoblasts, and concluded that reduced binding-protein interaction rather than increased receptor binding explained the difference [5]. A later report put LR3's type-1 receptor binding at about three-fold weaker than that of IGF-I [9].

What the structural studies show

Two NMR studies examined whether the modifications distort the protein.

Laajoki and colleagues first assigned the backbone and most side-chain resonances of 15N-labelled Long-[Arg3]-IGF-I and determined its secondary structure. The IGF-I domain was found to have an almost identical structure to IGF-I. Within the extension, the first seven residues showed very few medium- or long-range NOEs, while the next five formed a turn-like structure positioned close to the start of helix 1 of the IGF-I domain; many amide protons in the extension were nonetheless protected from solvent [4].

The same group then published a full solution structure with backbone dynamics [3]. Their findings, in their own terms:

  • The IGF-I domain of the analogue is consistent with earlier structures of IGF-I, with only minor changes remote from the N-terminus.
  • The major variation compared with IGF-I occurs at the N-terminus, including a substantial reorientation of the first three residues of the IGF-I domain. The authors interpreted this in terms of the analogue's lower binding affinity for the binding proteins.
  • The molecule is considerably flexible, including within the helices, and the N-terminal extension gives negative heteronuclear NOEs, indicating high mobility, although slow amide exchange for some residues suggests transient structure there.

Two points follow. The modification is local: the folded core is essentially that of IGF-I, which is why the analogue still engages the receptor at all. And the altered N-terminus is the structural explanation for the weakened binding-protein interaction, which is the property the molecule exists for.

Receptor binding, and why "more potent" is not a property of the molecule

It is common to see IGF-1 LR3 described as a more potent version of IGF-1. The primary literature does not support that as an unqualified statement: the difference depends on whether the experimental system contains binding proteins.

In the original comparison, Francis and colleagues tested their human IGF-I fusion analogues across several cell lines. In cell lines that secrete binding proteins into the medium, the order of biological potency was Long [Arg3]-IGF-I and des(1-3)IGF-I greater than Long [Gly3]-IGF-I, greater than Long IGF-I, greater than IGF-I. In chicken embryo fibroblasts, a line the authors reported does not secrete detectable binding proteins, the same human Long [Arg3]-IGF-I was less potent than IGF-I [2]. The variable there is the culture system, not the analogue: one molecule, opposite rankings, depending on whether binding proteins were present.

A second study reached a compatible conclusion with different material. Pesall and colleagues worked with a chicken LR3 IGF-I analogue, not the human one, and compared it with chicken IGF-I in turkey satellite cells and embryonic myoblasts in serum-free medium. The chicken analogue was significantly less active than chicken IGF-I in both cell types, and receptor-binding measurements in the same work showed it competed less well than chicken IGF-I for binding to those cells. The authors drew two conclusions: that binding proteins had little influence on type-1 receptor action in these particular cell types under those conditions, and that modifying the IGF molecule to prevent binding-protein interaction may also alter its receptor affinity [10].

The species distinction matters when reading these two results together. Francis 1992 concerns the human analogue, the molecule sold under the name IGF-1 LR3; Pesall 2001 concerns a chicken counterpart of it in avian cells. The second is supporting evidence for the general principle, not a second measurement of the same material, and neither study tested the lot described further down this page.

Taken together: IGF-1 LR3 trades receptor affinity for escape from binding proteins. Where binding proteins restrain IGF-I that trade is favourable and the analogue behaves as the more potent molecule; where they do not, the lost receptor affinity has nothing to offset it and the analogue can be the weaker one. Which case applies has to be established for the cells and medium in use, not assumed from the compound's reputation.

Documented laboratory applications

Serum-free mammalian cell culture

The best-documented application is as a growth and viability factor in serum-free culture of Chinese hamster ovary cells, the workhorse of recombinant protein production. Morris and Schmid compared insulin, the usual supplement, with LongR3 in two serum-free CHO lines expressing recombinant cytokine receptors. One line grew without any added growth factor, the other required either insulin or LongR3; both needed a growth factor for optimal performance under production conditions, and LongR3 sustained the viability of both lines better than insulin did [11].

Work published alongside it used native IGF-I rather than the analogue, and is worth separating for that reason: in attached CHO cultures IGF-I alone maintained viability for an extended period without serum but did not by itself stimulate proliferation, which also required transferrin [12]. That study characterises the IGF axis in these cells; it is not a result about LR3.

Culture systems where unrestrained IGF signalling is not an advantage

Thomas and colleagues cultured bovine preantral follicles for six days in serum-free medium with increasing concentrations of either LR3 IGF-I or human recombinant IGF-I. Both increased follicle diameter in a dose-dependent manner and raised estradiol production above control levels. However, follicles treated with LR3 IGF-I, and those given the highest concentration of native IGF-I, had smaller oocyte-to-follicle diameter ratios and increased oocyte degeneration compared with controls or with physiological concentrations of native IGF-I. Binding proteins were detected in the cultured follicles, and the authors concluded that regulation of IGF-I bioavailability by those proteins is necessary for coordinated oocyte and follicle development in vitro [13].

This is a useful counterweight to the idea that bypassing binding-protein control is simply an improvement: in this system that regulation was part of the biology under study, and removing it changed the outcome for the worse.

Recombinant production

Both IGF-1 and LR3 IGF-1 have been produced in Pichia pastoris as fusions with a highly expressed xylanase, reaching roughly 0.5 g/L and 1 g/L respectively in bioreactor fermentation, with the purified proteins reported to show cell-proliferation bioactivity comparable to a standard IGF-1 preparation [14]. This matters commercially as well as scientifically: material sold under this name may come from bacterial or yeast systems, with different fusion partners, tags and cleavage strategies, and those differences are invisible on a label.

The animal literature, in brief

A substantial part of the published work on this analogue was done in whole animals. Those studies investigated growth and metabolic endpoints, and their relevance to in vitro research is indirect; they are summarised here so that readers know the literature exists and what kind of literature it is.

ModelWhat was investigatedDirection of the reported result
Rats in a catabolic state [9][15]Body weight, nitrogen balance, gut massLR3 and des(1-3)IGF-I more potent than IGF-I
Pigs and marmoset monkeys [16]Acute blood-glucose responseVariants with poor binding-protein affinity more potent than IGF-I
Pigs of different ages [17]Growth rate, circulating IGFs and IGFBP-3Mixed: growth reduced in older pigs, increased in neonatal pigs
Growth-restricted fetal sheep [18]Fetal weight, insulin, glucose, amino acidsNo improvement in growth; circulating amino acids fell
A mouse model of Alzheimer's disease [19]Amyloid pathology, behaviour and memoryMixed: some plaque measures changed, cognitive measures did not

Three cautions apply to every row. Results belong to the species, age and physiological state studied, and the same compound produced opposite directions of effect in young and old animals of one species [17]. Some findings concern the binding-protein system's response rather than a direct action of the analogue [9]. And none of it carries across to cultured cells, to other species, or to humans. No human trial of IGF-1 LR3 was identified; the limitations section gives the exact scope of that statement.

Name versus molecule

One published case report is directly relevant to anyone handling material sold under this name. A doping-control laboratory analysed a black-market vial and identified its contents, by high-resolution mass spectrometry of the intact and digested protein and by immunoassay, as Long-R3-IGF-I carrying a hexahistidine tag on the C-terminus through a Leu-Glu linker; the authors noted that such tags are added during production to simplify purification and that the effects of the tagged protein have not been described [20]. A 2026 review likewise lists IGF-1 analogues, IGF-1 LR3 among them, as unregulated peptides marketed as research compounds and used for performance purposes [21].

The point for a laboratory is narrow: a product name does not establish a molecule, and only an identity measurement on the lot in hand says what is in the vial. This is the same reasoning we applied to a differently named component in our KLOW blend guide.

Reading our IGF-1 LR3 certificate

Our IGF1-LR3 1mg is currently shipped from lot PPL-IG1-1, and the certificate below is the third-party report for that lot. Two dates appear in our records and they mean different things: the certificate's printed certification date is August 9, 2026, and it was added to our COA Library on August 22, 2026. Neither is the date the laboratory performed the testing, which the certificate does not state.

What Kovera Labs reported for this lot:

TestReference on the certificateResult as printed
Batch average purity>98 %99.780 %
Batch average net content~1 mg1.04 mg
Identity confirmation (LC-MS)IGF-1 LR3IGF-1 LR3
Endotoxin safety screen≤0.5 EU/mLPASS

The purity and content figures are also given per vial: vial 1 at 99.767 % and 1.03 mg, vial 2 at 99.793 % and 1.06 mg. Two vials is a small sample; their agreement says something about consistency within this lot and nothing about vials that were not tested. The stated chromatography is RP-HPLC on a C18 column with diode-array detection at 214 nm.

Net content above the label figure is normal and is explained in our guide to purity versus net content: purity is a proportion of what was detected, net content is an absolute mass, and the two answer different questions. Our guide to reading a certificate of analysis covers the fields in general.

What the identity line does and does not establish

The certificate's identity row names the technique, LC-MS, and the expected compound, and records the result as confirmed. It does not print an observed numerical molecular mass, a theoretical mass to compare it against, a mass tolerance, or any sequence-level data.

That is a real limitation. For a recombinant protein of this size, a complete identity result would ordinarily show the measured intact mass against the calculated value for the intended sequence, with stronger evidence still coming from peptide mapping or fragmentation data confirming the sequence, including the 13-residue extension and the arginine at position 3. None of that appears here. We will not supply numbers the laboratory did not report: what can be said is that Kovera states it confirmed identity by LC-MS, and that a reader cannot independently check that conclusion from the document.

What the endotoxin line does and does not establish

The endotoxin row reports PASS against a reference of ≤0.5 EU/mL. It does not give a numerical result, name the test method, or state the reconstitution volume that an EU/mL figure would depend on. Without those, the result cannot be independently evaluated: a per-millilitre limit is not interpretable without knowing the concentration tested.

A PASS on this line means the laboratory considered the stated specification met. It is not evidence of sterility, it does not establish suitability for administration to humans or animals, and it carries no regulatory approval of any kind.

Limitations and open questions

  • Potency is context-dependent, not intrinsic. The analogue was less potent than native IGF-I in at least two published systems [2][10]. Anyone planning work with it should establish the behaviour in their own cells and medium.
  • Receptor affinity is reduced. Reports place it slightly to about three-fold below that of IGF-I [5][9]. Experiments that depend on receptor occupancy rather than on binding-protein escape may be a poor fit for this molecule.
  • Source material varies. Published production routes include bacterial and yeast systems with different fusion partners [2][14], and at least one marketed product was found to carry a histidine tag [20]. Identity data on the specific lot is the only way to address this.
  • Our certificate's identity and endotoxin rows are incomplete, as described above. We report them as printed.
  • Human research. We searched PubMed on November 7, 2026 for records on this analogue using the terms long R3 IGF, LR3 IGF-1, Long-[Arg3] IGF-I and author-based searches of the groups that developed it, and identified no controlled human trial of IGF-1 LR3. That statement is limited to PubMed on that date and to those queries; it does not cover other databases, conference abstracts or unpublished work. Human and clinical literature on native IGF-I is a separate body of work and its findings do not describe this analogue.
  • Sources read. The findings above were verified against the published abstracts and bibliographic records of each paper through PubMed, and quoted figures are those the abstracts state. Full texts were not obtained for this article, so results reported only in figures or supplementary material are not represented here.

Where to find the certificate

The Kovera Labs report for lot PPL-IG1-1 is in our COA Library under IGF1-LR3 1mg, and it is linked from the product page. If the lot printed on a vial you hold does not appear in the library, contact us with the lot number and we will locate the corresponding report.

Evidence from our lab reports

Each row is one certificate on file, identified by product and report date. Values are the figures the testing laboratory reported for that lot; they are not re-measured or adjusted here. "Latest COA in Library" and "Earlier COA" describe the certificate's place in the COA Library for that product. The lot currently shipping is identified by each product's inventory batch number, not by which certificate is newest.

ProductReport dateTestPurityNet contentCertificate
IGF1-LR3 1mgLatest COA in LibraryAug 22, 2026HPLC purity99.78%1.04 mg View

Frequently asked questions

What is IGF-1 LR3?
IGF-1 LR3 is a recombinant analogue of human insulin-like growth factor-I, known in the literature as Long-[Arg3]-IGF-I. It differs from the natural 70-residue protein in two defined ways: the glutamate at position 3 is replaced by arginine, and a 13-amino-acid extension is attached to the N-terminus. It was created as a research reagent to study how much of IGF-I's activity is controlled by IGF-binding proteins, and Precise Pep Labs sells it for in vitro research use only.
What does "LR3" stand for?
"L" refers to the Long form, meaning the 13-residue N-terminal extension, and "R3" to the arginine substituted at residue 3 of the IGF-I sequence. The extension originated as a fusion partner that improved folding and yield during expression in Escherichia coli and was retained rather than cleaved.
How does IGF-1 LR3 differ from native IGF-1?
Chain length and the N-terminus. Native IGF-I is 70 residues with a calculated molecular weight of 7,649; IGF-1 LR3 is 83 residues, with arginine at position 3. NMR solution structures show the folded IGF-I domain is essentially unchanged, with the major variation at the N-terminus, including a reorientation of the first three residues of the IGF-I domain. That region is where IGF-binding proteins contact the molecule.
Is IGF-1 LR3 more potent than IGF-1?
Not as a general property. In cell lines that secrete IGF-binding proteins into the medium, the human Long-[Arg3] analogue was among the most potent tested. In chicken embryo fibroblasts, reported not to secrete detectable binding proteins, that same analogue was less potent than IGF-I. A separate study of a chicken LR3 counterpart found it significantly less active than chicken IGF-I in turkey satellite cells and embryonic myoblasts. Reported type-1 receptor binding is weaker than that of IGF-I, so the comparison depends on the analogue, the cells and whether binding proteins are present.
Why do laboratories use IGF-1 LR3 in serum-free cell culture?
As a growth and viability supplement, particularly for Chinese hamster ovary cells used in recombinant protein production. In one published comparison with insulin, the usual supplement, LongR3 sustained the viability of two serum-free CHO lines better than insulin did under production conditions. Not every culture system benefits: in cultured bovine preantral follicles, LR3 IGF-I was associated with smaller oocyte-to-follicle ratios and increased oocyte degeneration compared with physiological concentrations of native IGF-I.
What does the certificate for our IGF-1 LR3 lot show?
Kovera Labs report KVR-2026-4E6B70 for lot PPL-IG1-1 gives a batch average purity of 99.780 % against a >98 % reference and a batch average net content of 1.04 mg against a ~1 mg label, from two vials measured individually, by RP-HPLC with detection at 214 nm. Identity is recorded as confirmed by LC-MS, but no observed molecular mass is printed, and the endotoxin row reports PASS against ≤0.5 EU/mL without a numerical result or a stated method. A PASS is not evidence of sterility or of suitability for administration.

References

  1. 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. PMID 632300. https://pubmed.ncbi.nlm.nih.gov/632300/
  2. Francis GL, Ross M, Ballard FJ, Milner SJ, Senn C, McNeil KA, et al. 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. 1992;8(3):213–223. doi:10.1677/jme.0.0080213
  3. Laajoki LG, Francis GL, Wallace JC, Carver JA, Keniry MA. Solution structure and backbone dynamics of long-[Arg(3)]insulin-like growth factor-I. Journal of Biological Chemistry. 2000;275(14):10009–10015. doi:10.1074/jbc.275.14.10009
  4. Laajoki LG, Le Breton E, Shooter GK, Wallace JC, Francis GL, Carver JA, et al. Secondary structure determination of 15N-labelled human Long-[Arg-3]-insulin-like growth factor 1 by multidimensional NMR spectroscopy. FEBS Letters. 1997;420(1):97–102. doi:10.1016/s0014-5793(97)01496-8
  5. King R, Wells JR, Krieg P, Snoswell M, Brazier J, Bagley CJ, et al. Production and characterization of recombinant insulin-like growth factor-I (IGF-I) and potent analogues of IGF-I, with Gly or Arg substituted for Glu3, following their expression in Escherichia coli as fusion proteins. Journal of Molecular Endocrinology. 1992;8(1):29–41. doi:10.1677/jme.0.0080029
  6. Ballard FJ, Wallace JC, Francis GL, Read LC, Tomas FM. Des(1-3)IGF-I: a truncated form of insulin-like growth factor-I. International Journal of Biochemistry & Cell Biology. 1996;28(10):1085–1087. doi:10.1016/1357-2725(96)00056-8
  7. Ballard FJ, Francis GL, Ross M, Bagley CJ, May B, Wallace JC. Natural and synthetic forms of insulin-like growth factor-1 (IGF-1) and the potent derivative, destripeptide IGF-1: biological activities and receptor binding. Biochemical and Biophysical Research Communications. 1987;149(2):398–404. doi:10.1016/0006-291x(87)90380-9
  8. Firth SM, Baxter RC. Cellular actions of the insulin-like growth factor binding proteins. Endocrine Reviews. 2002;23(6):824–854. doi:10.1210/er.2001-0033
  9. Tomas FM, Knowles SE, Owens PC, Chandler CS, Francis GL, Read LC, et al. Insulin-like growth factor-I (IGF-I) and especially IGF-I variants are anabolic in dexamethasone-treated rats. Biochemical Journal. 1992;282(Pt 1):91–97. doi:10.1042/bj2820091
  10. Pesall JE, McFarland DC, McMurtry JP, Clapper JA, Francis GL, Gilkerson KK. The effect of insulin-like growth factor analogs on turkey satellite cell and embryonic myoblast proliferation. Poultry Science. 2001;80(7):944–948. doi:10.1093/ps/80.7.944
  11. Morris AE, Schmid J. Effects of insulin and LongR(3) on serum-free Chinese hamster ovary cell cultures expressing two recombinant proteins. Biotechnology Progress. 2000;16(5):693–697. doi:10.1021/bp0000914
  12. Sunstrom NA, Gay RD, Wong DC, Kitchen NA, DeBoer L, Gray PP. Insulin-like growth factor-I and transferrin mediate growth and survival of Chinese hamster ovary cells. Biotechnology Progress. 2000;16(5):698–702. doi:10.1021/bp000102t
  13. Thomas FH, Campbell BK, Armstrong DG, Telfer EE. Effects of IGF-I bioavailability on bovine preantral follicular development in vitro. Reproduction. 2007;133(6):1121–1128. doi:10.1530/REP-06-0382
  14. Lu Z, Liu N, Huang H, Wang Y, Tu T, Qin X, et al. Recombinant expression of IGF-1 and LR3 IGF-1 fused with xylanase in Pichia pastoris. Applied Microbiology and Biotechnology. 2023;107(14):4543–4551. doi:10.1007/s00253-023-12606-0
  15. Read LC, Tomas FM, Howarth GS, Martin AA, Edson KJ, Gillespie CM, et al. Insulin-like growth factor-I and its N-terminal modified analogues induce marked gut growth in dexamethasone-treated rats. Journal of Endocrinology. 1992;133(3):421–431. doi:10.1677/joe.0.1330421
  16. Tomas FM, Walton PE, Dunshea FR, Ballard FJ. IGF-I variants which bind poorly to IGF-binding proteins show more potent and prolonged hypoglycaemic action than native IGF-I in pigs and marmoset monkeys. Journal of Endocrinology. 1997;155(2):377–386. doi:10.1677/joe.0.1550377
  17. Walton PE, Dunshea FR, Ballard FJ. In vivo actions of IGF analogues with poor affinities for IGFBPs: metabolic and growth effects in pigs of different ages and GH responsiveness. Progress in Growth Factor Research. 1995;6(2–4):385–395. doi:10.1016/0955-2235(95)00007-0
  18. White A, Stremming J, Wesolowski SR, Al-Juboori SI, Dobrinskikh E, Limesand SW, et al. IGF-1 LR3 does not promote growth in late-gestation growth-restricted fetal sheep. American Journal of Physiology: Endocrinology and Metabolism. 2025;328(1):E116–E125. doi:10.1152/ajpendo.00259.2024
  19. Engel MG, Narayan S, Cui MH, Branch CA, Zhang X, Gandy SE, et al. 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. 2025;103(1):113–126. doi:10.1177/13872877241299056
  20. Kohler M, Thomas A, Walpurgis K, Terlouw K, Schänzer W, Thevis M. Detection of His-tagged Long-R3-IGF-I in a black market product. Growth Hormone & IGF Research. 2010;20(5):386–390. doi:10.1016/j.ghir.2010.07.001
  21. Dominikowski A, Rękoś Z, Olejarz M, Szczepanek-Parulska E, Domin R, Ruchała M. The emerging landscape of performance-enhancing peptides modulating GH-IGF1 axis: bridging the gap between clinical evidence and patient self-administration. Frontiers in Endocrinology. 2026;17:1822475. doi:10.3389/fendo.2026.1822475

How this article was checked

  • Written by: Precise Pep Labs Research Editorial Team
  • Last reviewed: November 7, 2026
  • Published: November 7, 2026
  • Last updated: November 7, 2026
  • Lab reports cited: 1
  • Sources: the numbered references above and the certificates of analysis in the COA Library. Editorial content is reviewed for research-use-only compliance before publication.

Related research materials

Reference materials discussed in this article, each with its certificate of analysis

IGF1-LR3 1mg vial

IGF1-LR3

1mg
$64.99

Related articles