Two changes, one purpose
Native IGF-1 circulates almost entirely bound to a family of binding proteins, which regulate how much is free to act at any moment. The LR3 variant carries an amino acid substitution plus a thirteen-residue extension at the N-terminus.
Both modifications reduce its affinity for those binding proteins. The result stays free far longer than the natural molecule, which is precisely what it was designed to do.
The extension sits at the front of the molecule, where the binding proteins make contact. Adding residues there and altering one more inside the contact region is enough to weaken the interaction substantially, which is a tidy demonstration of how small a patch of protein surface a regulatory mechanism can depend on.
Why the binding proteins exist in the first place
That regulatory system is not an obstacle the body accidentally left in place. IGF-1 signalling touches cell growth and proliferation broadly, and binding proteins are how the amount of active signal is controlled.
A molecule built to bypass that control removes a brake. Whatever else it does, that is what it does first, and it is the reason this compound is discussed very differently in the literature than in forums.
The variant does have a legitimate home, and it is worth naming. It is used as a supplement in cell culture, where a growth factor that stays available instead of being captured by binding proteins in the medium is exactly what an experiment needs. That is a controlled setting with a defined purpose, and it is a long way from a vial offered to a general audience.
| Full name | Long R3 insulin-like growth factor 1 |
| Modifications | Residue substitution plus 13-residue N-terminal extension |
| Effect of modification | Reduced binding-protein affinity |
| Consequence | Stays free far longer than native IGF-1 |
| Stocked here | No, and not planned |
| Closest alternative | GH secretagogues, acting upstream |
| Evidence base | Laboratory and animal work |
| Category | Research use only |
Descriptive specification only, with no implied result.
We do not supply IGF-1 LR3
It is not a compound we are willing to put in a catalogue aimed at a general research audience, and we would rather say so on the page than not have the page.
If the underlying interest is growth hormone research, the secretagogues work upstream on the body’s own release, which is a different proposition entirely. Those pages are linked below.
So the answer to what is IGF-1 LR3 comes in two halves that are almost never given together: a well-characterised laboratory reagent, and a molecule engineered to remove a control mechanism. The muscle and performance area explains why the second half keeps it out of this catalogue while the secretagogues stay in it.
Sequence, variant and the certificate
A modified protein raises a documentation question that a short synthetic peptide does not. The paperwork has to establish which variant is present, not only how pure the sample is, because the native molecule and the extended one differ by a handful of residues and both can present as a single clean peak if the method was not chosen to separate them. That is one of the situations the page on purity figures was written for.
The reference record for the native protein sits on UniProt, which is the sensible starting point if you want the sequence the variant was built from rather than a supplier’s paraphrase of it.
The research literature is large and mostly concerns the native system. Searching the indexed work on PubMed for the variant returns a much narrower set, weighted heavily towards cell-culture methodology. Where growth signalling in muscle tissue is the real interest, the follistatin 344 page covers a different mechanism aimed at the same place.
IGF-1 LR3 in the catalogue
A 99% HPLC minimum, checked per lot rather than per shipment.
Where IGF-1 LR3 fits in
The nearest topics, in three links.
About IGF-1 LR3
The recurring queries about this one.