Quick answer: IGF-1 LR3 ("long R3 IGF-1") is a synthetic 83-amino-acid analog of insulin-like growth factor 1, with an arginine substituted for glutamate at position 3 and a 13-residue extension at the N-terminus. Those changes make it bind IGF-binding proteins far less than natural IGF-1, so it is more potent in cell culture. Its main established laboratory use is as a growth-factor supplement in cell culture media, and it is sold here for laboratory research only.
What IGF-1 LR3 is
Insulin-like growth factor 1 (IGF-1) is a 70-amino-acid protein hormone that acts on the IGF-1 receptor to drive cell growth and survival signalling. In biological fluids most IGF-1 is bound to a family of carrier proteins, the IGF-binding proteins, which hold it in reserve and limit how much is free to act on cells. That is useful in the body, but it is a nuisance in a culture dish, where binding proteins in the medium soak up added IGF-1.
IGF-1 LR3 was engineered around that problem. It is an 83-residue analog: LR3 stands for "long R3": the R3 is the arginine that replaces glutamate at position 3, and "long" refers to the 13-amino-acid extension at the N-terminus. Together these changes sharply reduce binding to IGF-binding proteins while preserving activity at the IGF-1 receptor, so the analog stays free and active at lower concentrations. Our structure and synthesis article covers the sequence in detail.
What "igf peptide" searches are really about
People search for "igf peptide", "igf-1" and "igf1 lr3", and the three are related but not identical. IGF-1 is the natural hormone, a 70-residue protein. IGF-1 LR3 is the engineered analog above. Some sellers also list shorter fragments or other analogs under similar names, which makes a vague listing risky. The only dependable identifier is the declared compound name, the length and the molecular weight on the certificate. We supply IGF-1 LR3 as a 1 mg research vial.
Where it is used in the laboratory
IGF-1 LR3 has a long history as a media supplement in cell culture. It is added to serum-free and low-serum media to support the growth and survival of cell lines, including those used in the manufacture of biological products, because it stays active when natural IGF-1 would be neutralized by binding proteins. In research settings it is also used to study IGF-1 receptor signalling, including the PI3K and MAPK pathways, in cell and tissue models.
These are laboratory uses. This guide makes no claims about what the compound does in people or animals. Our mechanism of action article describes the signalling in more detail, and the research overview summarizes how it is used.
Why an 83-residue protein is harder to verify
IGF-1 LR3 is large for a research peptide and contains three disulfide bonds that hold its folded shape. Correct folding matters, because a mis-folded sample can have the right amino acid sequence and still be inactive. A standard HPLC run shows purity of the chain, but it does not by itself prove correct folding.
That makes the documentation for this compound more demanding than for a short peptide. Good reports state measured purity with the chromatogram, confirm identity, and give a measured quantity per vial. Because it is supplied at only 1 mg, the quantity check matters: a few tenths of a milligram of error is a large percentage. Our IGF-1 LR3 purity testing article explains the issues, and understanding HPLC purity covers the trace.
What to check on an IGF-1 LR3 listing
- The exact compound. The listing should say LR3 and give the length (83 residues), not just "IGF-1".
- A certificate for the lot, naming lot code, test date and laboratory.
- Measured HPLC purity with the chromatogram attached.
- Measured content per vial, compared with the 1 mg label.
- Endotoxin and sterility, which matter for any cell culture use.
- Verifiability with the issuing laboratory.
If the format is unfamiliar, how to read a COA walks through a certificate line by line. Our supplier checklist is in how to choose a research peptide supplier, and the sourcing notes for this compound are in where to buy IGF-1 LR3.
Common points of confusion
Several mix-ups are common. First, IGF-1 is not the same as human growth hormone. Growth hormone prompts the liver and other tissues to make IGF-1, which is a downstream signal, and the two are different molecules acting on different receptors. Second, IGF-1 LR3 is not the natural hormone: its engineered sequence changes how it behaves around binding proteins, so results with LR3 do not transfer directly to IGF-1 itself. Third, listings sometimes use "IGF-1" for shorter fragments or other analogs, which are different compounds with different properties. Always match the length and name on the label to the certificate.
Reading the literature carefully
Most published work that mentions IGF-1 LR3 uses it as a tool, not as the subject, so the useful details are in the methods section: the cell type, the medium, the concentration range, the presence or absence of serum, and how long cells were exposed. Papers that omit those details are hard to reproduce. When you compare results between laboratories, check that the same analog was used, since natural IGF-1 and LR3 behave differently around binding proteins, and a concentration that works for one may be far too high or too low for the other.
Planning small-quantity work
At 1 mg per vial, practical details dominate. Losses to the vial wall and pipette tips are a larger fraction of the total than they would be with a 10 mg vial, so many laboratories reconstitute the whole vial at once, add a carrier protein, and divide the stock into single-use aliquots to avoid repeated freeze and thaw cycles. They also check the concentration they actually made, not just the one they calculated. The calculator guide helps with the arithmetic, and the general reconstitution guide covers technique.
Where the name comes from
The name is worth unpacking because sellers use it loosely. IGF-1 is the natural 70-residue hormone. The "LR3" analog was developed by researchers who wanted a form of IGF-1 that cells could use in the presence of binding proteins. It was commercialized as a cell culture supplement and has been used that way for years in laboratory and biomanufacturing work. When you read a listing, the question to ask is whether the label says LR3, whether it gives the 83-residue length, and whether the certificate matches. Our discovery and history article tells the full story.
Storage and handling
The compound is supplied as a lyophilized powder. General laboratory practice is to keep the sealed vial refrigerated, protected from light, heat and moisture, and to avoid repeated temperature cycling. Proteins of this size are prone to sticking to plastic and to losing activity in dilute solution, so many laboratories add a carrier protein to stock solutions and make small aliquots. The reconstitution and storage article has the details, and the calculator guide helps with concentration arithmetic at this small scale.
What V8 Peptides publishes for IGF-1 LR3
We supply IGF-1 LR3 as a 1 mg research vial. We have not yet published a certificate for this product. We have asked our laboratory supply chain for reports on every product that lacks one, and IGF-1 LR3 is on that list. When it arrives it will go on the COA page and the product page will be updated. The certificates we do have can be verified directly on the laboratory's own site.
Frequently asked questions
What does LR3 mean in IGF-1 LR3?
The R3 is an arginine replacing glutamate at position 3, and the long part is a 13-amino-acid N-terminal extension. Together they reduce binding to IGF-binding proteins.
Is IGF-1 LR3 the same as IGF-1?
No. IGF-1 is the natural 70-residue hormone. IGF-1 LR3 is an engineered 83-residue analog that binds carrier proteins far less.
What is it used for in the laboratory?
Mainly as a growth-factor supplement in cell culture media, and in studies of IGF-1 receptor signalling in cell and tissue models.
Why is it harder to verify than a short peptide?
It is an 83-residue protein with three disulfide bonds. Purity by HPLC does not prove correct folding, so identity and content matter too.
What should a COA show?
Lot code, test date, laboratory, measured HPLC purity with the chromatogram, identity, measured content against the 1 mg label, and endotoxin and sterility results.
Does V8 Peptides publish a COA for IGF-1 LR3?
Not yet. We have requested one and will post it on the COA page when it arrives.
How should it be stored?
General practice is refrigeration of the sealed vial, protected from light, heat and moisture, with small aliquots of stock solutions.
Is this guide advice for use in people?
No. IGF-1 LR3 is supplied for laboratory research only, and nothing here is guidance for use in people or animals.
Where to go next
For a fuller picture of the compound, start with the IGF-1 LR3 research overview and the research FAQ. To check the certificates we publish, visit the COA page.
References
- Laron Z. Insulin-like growth factor 1 (IGF-1): a growth hormone. Molecular Pathology. 2001;54(5):311-316.
- Baxter RC. Insulin-like growth factor (IGF)-binding proteins: interactions with IGFs and intrinsic bioactivities. American Journal of Physiology: Endocrinology and Metabolism. 2000;278(6):E967-E976.
- Bach LA. IGF-binding proteins. Journal of Molecular Endocrinology. 2018;61(1):T11-T28.
For laboratory research use only. Not for human or animal consumption. Not a drug, food or cosmetic. This article is educational and describes published research; it makes no claims about outcomes in people or animals.