What does the "LR3" in IGF-1 LR3 stand for?

It is a compression of the two modifications. "R3" refers to the substitution of arginine for the glutamic acid normally found at position 3 of the chain, and "Long" refers to the 13-residue extension added to the N-terminus. Put together, Long R3 IGF-1 names an analogue that differs from native insulin-like growth factor 1 at both the third residue and the beginning of the chain. The abbreviation is unusually informative as research-compound names go, because it describes the chemistry rather than being a code number.

How is IGF-1 LR3 different from native IGF-1?

Native human IGF-1 is a 70-residue protein. IGF-1 LR3 is 83 residues, carrying both the N-terminal extension and the arginine substitution at position 3. The functional consequence described in the literature is reduced affinity for the IGF-binding proteins that normally associate with circulating IGF-1. In a culture system those binding proteins would otherwise sequester a substantial fraction of what you add, so an analogue that evades them behaves more predictably at a given concentration. That predictability, not potency as such, is the reason the analogue exists.

What is IGF-1 LR3 used for in laboratory research?

Its most common documented role is as a component of serum-free or reduced-serum cell culture media, where a defined growth-factor input replaces the undefined mixture that serum provides. It is also studied directly as an agonist at the IGF-1 receptor in work on that receptor and its downstream signalling. Observations depend entirely on the cell type, the concentration, the exposure time and the rest of the medium, and are properties of the experimental system rather than general effects.

Is IGF-1 LR3 a peptide?

Not in the sense that most compounds discussed on this site are. At 83 amino acids and roughly 9 kDa it sits in protein territory, where folding and tertiary structure matter, rather than in the short linear-peptide range of 3 to 30 residues. The practical difference is in handling: proteins of this size are more sensitive to surface adsorption, freeze-thaw cycling and agitation than a small peptide, and they are considerably harder to characterise analytically.

Do you sell IGF-1 LR3?

No. We do not stock IGF-1 LR3, there is no Certificate of Analysis for it in our library, and this guide is not an offer to supply it. It is covered here because the question gets asked often enough to deserve an accurate answer from somewhere other than a shop listing.

What is IGF-1 LR3?

7 min read · Updated October 2026 · MY PEPTIDES Research Team

Key facts

IGF-1 LR3, written in full as Long R3 insulin-like growth factor 1, is a synthetic analogue of human IGF-1 rather than the native protein. It differs in two deliberate ways: the glutamic acid at position 3 is replaced with arginine, and a 13-residue extension is added to the N-terminus, giving a chain of 83 amino acids against the 70 of native IGF-1. Both changes reduce how readily the molecule is bound by IGF-binding proteins, which is the specific property that makes it useful in cell-culture work: more of what is added to a medium stays available to the receptor rather than being sequestered. In laboratory research it is studied as an agonist at the IGF-1 receptor and appears widely as a supplement to serum-free culture media. It is a protein-scale molecule of roughly 9 kDa, not a short peptide, and it is handled accordingly. MY PEPTIDES does not stock IGF-1 LR3. This is general information for in-vitro laboratory context only, not medical advice.

The short answer

IGF-1 LR3 is not insulin-like growth factor 1. It is a deliberately modified version of it, built to evade the binding proteins that would otherwise mop up most of a dose in a culture system. Two changes do that work: arginine replaces the glutamic acid at position 3, and a 13-residue tail is bolted onto the N-terminus. The result is 83 amino acids where native IGF-1 has 70.

That is the whole compound in a sentence, and it explains why it exists. Nobody designed IGF-1 LR3 to be a better growth factor. They designed it to be a more predictable one in a dish.

What the modifications actually do

Native IGF-1 does not circulate freely. It travels bound to a family of IGF-binding proteins, which control how much of it is available to the receptor at any moment. That regulation is useful in an organism and a nuisance in an experiment: add native IGF-1 to a culture medium containing those binding proteins and an unknown fraction of it is immediately unavailable, so the concentration you intended is not the concentration the cells experience.

Both modifications in Long R3 IGF-1 reduce how readily those binding proteins associate with the molecule. The literature describes the analogue as substantially less susceptible to that sequestration than the native protein. For a researcher the consequence is straightforward: the figure written in the protocol is much closer to the figure acting on the receptor, and results are more reproducible between runs and between laboratories.

It is worth being precise about the claim being made here. Reduced binding-protein affinity is a statement about the molecule's behaviour in a defined system. It is not a claim about anything happening in a person, and this guide makes none.

A protein, not a short peptide

Most compounds in this field are short linear chains of three to thirty residues. At 83 residues and around 9 kDa, IGF-1 LR3 is an order of magnitude larger, and that changes almost everything practical about it.

Short peptides are robust: they have little secondary structure to lose, and their integrity is largely a question of whether the bonds are intact. A protein of this size has a folded conformation that it needs in order to work. It can be denatured by heat, by agitation, by repeated freezing and thawing, and by simple adsorption onto the walls of a plastic tube at low concentrations. None of those insults necessarily shows up in a purity assay, because the chain can be entirely intact and the molecule still inactive.

That is why protein-scale reagents normally arrive with handling instructions that look fussier than they are: carrier protein in the buffer to limit adsorption, single-use aliquots instead of repeated entry, and a firm instruction not to vortex. The general principles in our guide on storing research peptides apply, but a 9 kDa protein is the demanding end of that spectrum rather than the easy end.

How it appears in the research literature

Two uses dominate. The first is as a defined medium component. Serum is cheap and effective and chemically a black box; replacing it with named growth factors at known concentrations is what lets a culture experiment be described precisely enough for someone else to repeat. IGF-1 LR3 appears in that role across a wide range of cell types, and the binding-protein resistance is the reason it is chosen over native IGF-1.

The second is as a tool for studying the IGF-1 receptor itself and the signalling that follows from it. Here the analogue is the instrument rather than the subject: you want reliable receptor engagement at a known concentration so that what you measure downstream can be attributed to that engagement.

In both cases the observations belong to the system being studied. Cell type, passage number, concentration, exposure time, medium composition and the presence or absence of other factors all change the result, which is why published work specifies them and why a general statement about what this compound "does" would be close to meaningless.

What the research does not establish

Searches for this compound frequently arrive carrying assumptions from outside the laboratory literature, so it is worth marking the boundary clearly.

Work in cell culture and in preclinical models does not establish effects in humans. A growth factor that engages its receptor in a dish tells you about receptor pharmacology, not about outcomes in a person, and the step between those two is exactly where most candidate compounds fail. There is no approved human medicine corresponding to IGF-1 LR3, and nothing in the in-vitro literature should be read as implying there is a safe or effective human application.

Where MY PEPTIDES stands

We do not stock this compound. There is no Certificate of Analysis for it in our library and no product page for it on this site, and this guide should not be read as an offer to supply it. If that changes, it will change by a product appearing in the catalogue with a batch certificate attached, not by a line in a guide.

The reason for saying so explicitly is that a page like this is otherwise easy to misread. Search for an obscure compound and most of the results are shops; an informational page from a supplier invites the assumption that the supplier sells it. We would rather answer the question and be clear about the answer to "can I buy it here", which is no.

What we do supply, and the documentation standard we hold it to, is set out in our guide on certificates of analysis.

The bottom line

IGF-1 LR3 is a modified, 83-residue analogue of insulin-like growth factor 1, engineered to evade the binding proteins that make native IGF-1 awkward to dose in culture. It is best understood as a laboratory reagent for defined media and receptor work, with handling requirements closer to those of a protein than a peptide. We do not supply it.

All compounds referenced on this site are discussed strictly in the context of in-vitro laboratory research. Nothing here is a medicine, a supplement or a therapeutic product, nothing here describes administration to humans or animals, and this guide is general information rather than medical, legal or research advice.

Frequently asked questions

What does the "LR3" in IGF-1 LR3 stand for?: It is a compression of the two modifications. "R3" refers to the substitution of arginine for the glutamic acid normally found at position 3 of the chain, and "Long" refers to the 13-residue extension added to the N-terminus. Put together, Long R3 IGF-1 names an analogue that differs from native insulin-like growth factor 1 at both the third residue and the beginning of the chain. The abbreviation is unusually informative as research-compound names go, because it describes the chemistry rather than being a code number.
How is IGF-1 LR3 different from native IGF-1?: Native human IGF-1 is a 70-residue protein. IGF-1 LR3 is 83 residues, carrying both the N-terminal extension and the arginine substitution at position 3. The functional consequence described in the literature is reduced affinity for the IGF-binding proteins that normally associate with circulating IGF-1. In a culture system those binding proteins would otherwise sequester a substantial fraction of what you add, so an analogue that evades them behaves more predictably at a given concentration. That predictability, not potency as such, is the reason the analogue exists.
What is IGF-1 LR3 used for in laboratory research?: Its most common documented role is as a component of serum-free or reduced-serum cell culture media, where a defined growth-factor input replaces the undefined mixture that serum provides. It is also studied directly as an agonist at the IGF-1 receptor in work on that receptor and its downstream signalling. Observations depend entirely on the cell type, the concentration, the exposure time and the rest of the medium, and are properties of the experimental system rather than general effects.
Is IGF-1 LR3 a peptide?: Not in the sense that most compounds discussed on this site are. At 83 amino acids and roughly 9 kDa it sits in protein territory, where folding and tertiary structure matter, rather than in the short linear-peptide range of 3 to 30 residues. The practical difference is in handling: proteins of this size are more sensitive to surface adsorption, freeze-thaw cycling and agitation than a small peptide, and they are considerably harder to characterise analytically.
Do you sell IGF-1 LR3?: No. We do not stock IGF-1 LR3, there is no Certificate of Analysis for it in our library, and this guide is not an offer to supply it. It is covered here because the question gets asked often enough to deserve an accurate answer from somewhere other than a shop listing.