IGF-1 LR3 is a laboratory designation, not a chemical name. This reference covers the identity of IGF-1 LR3: what the sequence is, how it differs from the native protein it is modelled on, what mass to expect, how a molecule of this size behaves under reverse-phase HPLC, and how a buyer can confirm that the material in a vial is what the label says. It does not describe what IGF-1 LR3 does, and it contains no guidance on preparation, handling or dosing.
The sequence behind IGF-1 LR3
IGF-1 LR3 is an 83-residue analogue of human insulin-like growth factor 1 (IGF-1). The native mature protein is 70 residues long. The analogue differs from it in two ways:
- a 13-residue N-terminal extension, Met-Phe-Pro-Ala-Met-Pro-Leu-Ser-Ser-Leu-Phe-Val-Asn (MFPAMPLSSLFVN), added in front of the native sequence;
- an arginine in place of glutamic acid at position 3 of the native IGF-1 numbering.
The full chain in one-letter code is:
MFPAMPLSSLFVNGPRTLCGAELVDALQFVCGDRGFYFNKPTGYGSSSRRAPQTGIVDECCFRSCDLRRLEMYCAPLKPAKSA
The native IGF-1 portion begins at the glycine immediately after the extension; in native IGF-1 it reads Gly-Pro-Glu-Thr, and in the analogue it reads Gly-Pro-Arg-Thr. The chain contains six cysteines, which in the correctly folded molecule form three disulfide bonds, as in the native protein. The average molecular mass is a little over 9.1 kDa.
What the name IGF-1 LR3 refers to
The name is shorthand for the two modifications. “Long” refers to the N-terminal extension and “R3” to the arginine at position 3. It is sometimes written Long R3 IGF-I or LR3 IGF-1; these are the same molecule. It is not the same as native IGF-1, and it is not the same as the variant that carries only the position-3 substitution without the extension, which is 70 residues long and correspondingly lighter.
At 83 residues, IGF-1 LR3 is closer in size to a small protein than to the short peptides elsewhere in this series, and a molecule of this length is normally produced by recombinant expression rather than stepwise chemical synthesis. That changes what an analysis has to show, as the next sections explain.
How IGF-1 LR3 behaves on reverse-phase HPLC
Proteins of this size are analysed on reverse-phase columns too, but with wider-pore packings — typically 300 angstrom C4 or C8 rather than the narrower-pore C18 used for short peptides — so that the folded chain can reach the bonded phase. With a water/acetonitrile gradient and trifluoroacetic acid, IGF-1 LR3 elutes late and as a single main peak when the material is homogeneous and correctly folded.
The sequence contains several tyrosines and phenylalanines and no tryptophan, so absorbance at 280 nm is present but moderate. Purity is normally read at around 214 nm, where the peptide backbone absorbs strongly.
The species that matter here are protein-type variants rather than simple deletion sequences. Mis-paired or incompletely formed disulfide bonds give isoforms that elute at slightly different positions from the main peak. The methionines — two in the extension and one in the native portion — can oxidise, each adding 16 daltons. Clipped forms missing part of the extension can also appear. A well-resolved chromatogram separates these as shoulders or small neighbouring peaks, and our guide to reading an HPLC chromatogram covers how to spot them.
What an analysis for IGF-1 LR3 should show
A useful certificate reports the column chemistry, pore size and dimensions, the mobile phase and gradient, the detection wavelength, the retention time, the integrated peak area with the integration window visible, and a mass confirmation. For a molecule of this size the mass confirmation is an intact-mass measurement: electrospray produces a ladder of multiply charged ions, which is deconvoluted to a single neutral mass. That figure should sit a little above 9.1 kDa. A result 2, 4 or 6 daltons higher than expected suggests that one or more disulfide bonds are not formed; a result 16 or 32 daltons higher suggests oxidised methionine. Our article on mass spectrometry and peptide identity explains deconvolution in more detail.
The certificate should also state net peptide content separately from chromatographic purity and name the counter-ion or buffer salt present. For a recombinant protein, residual buffer components and counter-ions from purification can make up a meaningful share of the powder, so the purity figure and the content figure answer different questions. Our explainer on peptide purity vs net peptide content sets out the difference.
Confirming identity independently
Look IGF-1 LR3 up by its sequence rather than by its trade name. Public protein databases catalogue native human IGF-1, and aligning the 83-residue sequence above against it will show the 13-residue extension and the single substitution at position 3 directly. Then compare the deconvoluted intact mass on the published analysis with the value expected for the fully disulfide-bonded chain. A mass well below 9 kDa, close to that of the native 70-residue protein, points to a different molecule.
How IGF-1 LR3 is supplied here
IGF-1 LR3 1mg is supplied as a lyophilised powder in a sealed vial. The published result for IGF-1 LR3 comes from independent reverse-phase HPLC. Both the vial size and the published HPLC purity of IGF-1 LR3 appear on the product page. There is no lot number on a IGF-1 LR3 vial, so the crimp and cap color are what tie it to the published result.
Frequently asked questions
How long is IGF-1 LR3?
83 residues: the 70 residues of human IGF-1 with glutamic acid 3 replaced by arginine, plus a 13-residue N-terminal extension.
What does “LR3” stand for?
“Long” for the N-terminal extension and “R3” for the arginine at position 3 of the native numbering.
What molecular weight should I expect for IGF-1 LR3?
A little over 9.1 kDa for the intact, disulfide-bonded chain. Published figures differ slightly with the calculation method, so compare against the expected value stated with the analysis.
Why is a C4 column used instead of C18?
Wide-pore, shorter-chain phases give sharper peaks and more complete elution for protein-sized molecules, which can bind too strongly or too slowly to narrow-pore C18 packings.
Research use only. All products supplied by Battle Born Peptides are laboratory reference materials for in-vitro research and analytical use by qualified professionals. They are not drugs, foods, dietary supplements, cosmetics or medical devices; they are not approved by the FDA or any other regulator for use in humans or animals; and they are not intended to diagnose, treat, cure, mitigate or prevent any disease, or to affect the structure or any function of the body of humans or animals. Nothing in this article is preparation, handling or dosing guidance. See our full research-use terms.