Most of what this site says about certificates assumes a synthetic peptide: a chain built on a resin, purified by chromatography, checked by mass. IGF-1 LR3 breaks that assumption, and the ways it breaks it are the useful content of this page.
What the name encodes
Insulin-like growth factor 1 is a 70-residue protein. LR3 describes two changes to it: a 13-residue extension on the N-terminus, which is the "L" for Long, and an arginine substituted at position three, which is the "R3". The result is 83 residues.
The substitution is the point of the design. Native IGF-1 circulates bound to a family of binding proteins that control how much is free, and analogues with reduced affinity for those binding proteins behave differently in a culture system for that reason alone. (Reference: Cascieri et al., 1991) Work on Long [R3] IGF-I specifically describes an analogue with reduced binding-protein affinity. (Reference: Dunaiski et al., 1997)
Why it is not made the way a peptide is
At 83 residues this is beyond the comfortable range of stepwise solid-phase synthesis. Every coupling step carries a chance of not finishing, and those chances compound, so a chain this long made residue by residue would arrive buried in deletion sequences.
It is produced recombinantly instead: the sequence is expressed in cells and purified from what they make. That changes the entire impurity picture. A synthetic peptide's impurities are chemical relatives of the target, mostly deletions and incomplete deprotections. A recombinant protein's impurities are host cell proteins, host DNA, and misfolded or truncated forms of the product.
So the certificate asks different questions
Purity by RP-HPLC still applies and still means the share of detected peak area that is the target. What it will not catch is a correctly sized chain folded wrongly, because folding is not something a reversed-phase column reports on.
Three fields matter here that are meaningless on a short synthetic peptide. Host cell protein and residual DNA are byproducts of the production system, and they have no equivalent in solid-phase synthesis. Endotoxin rises in importance because bacterial expression systems are a direct source of it, and endotoxin activates immune signalling at very low concentrations in cultured cells. (Reference: Raetz & Whitfield, 2002) Our note on endotoxins explains why ordinary sterilisation does not remove it.
A certificate that reports only HPLC purity and a mass for a recombinant protein is using a peptide template on something that is not a peptide.
Where the boundary between peptide and protein sits
There is no chemical line at which a chain stops being a peptide. The convention puts the change somewhere around fifty residues, and it is a rough marker for a real shift: short chains stay flexible in solution, longer ones have enough internal interactions to hold a stable fold. Our note on amino acids, peptides and proteins covers the distinction.
At 83 residues this molecule sits on the protein side of that convention, and the practical consequence is the one that matters: a folded structure can be right or wrong, and whether it is right is a question none of the usual peptide measurements answer. A short peptide has no fold to get wrong.
A CAS number that does not survive a lookup
This product was listed here with CAS 946870-92-4. That number passes the check digit, so our validator accepts the arithmetic. Looking it up is a different matter: in PubChem it resolves to an ionizable lipid with the formula C80H154N4O6S2, a compound unrelated to IGF-1 in every respect.
We removed it from the listing instead of leaving a number pointing at the wrong molecule. This is the exact failure our validator page warns about: the arithmetic never sees the compound name, so a real CAS number paired with the wrong substance passes every time. The second step, looking the number up and reading back what it returns, is the one that catches it.
Large recombinant proteins frequently lack a clean small-molecule registry entry, which is an ordinary fact about how those registries work, not a problem with the material. The honest position is to say there is no verified number instead of supplying one that resolves elsewhere.
What that leaves for identity
Without a public registry record, identity rests on what the certificate measures. For a protein this size that usually means a mass measurement with wider tolerance than a short peptide allows, since the isotope envelope of a nine-kilodalton molecule is broad, plus sequence confirmation by peptide mapping, where the protein is cut into fragments and those fragments are identified.
Our note on mass spectrometry covers the comparison of observed against theoretical mass. The principle carries over; the precision does not, and a tolerance quoted for a short peptide would be meaningless here.
Storage, for a molecule that can unfold
The degradation routes that affect peptides apply here too, and with 83 residues there is more chain for them to work on: hydrolysis of the backbone, deamidation, oxidation of susceptible side chains, all proceeding with time and temperature. (Reference: Manning et al., 2010)
A folded protein adds a route a peptide does not have. It can lose its structure without losing a single atom, which means a mass measurement after the fact would look unchanged. That is the argument for treating handling as part of what you are buying, not as something the certificate covers, and our note on storage sets out the chemistry.
Research use only
All products sold by Codex Research are strictly for laboratory research and development. They are not for human or animal consumption and are not intended to diagnose, treat, cure, or prevent any disease.
The compound at Codex Research
IGF-1 LR3, 1 mg per vial · batch-verified, with its certificate of analysis.
Frequently asked questions
What does LR3 mean in IGF-1 LR3?
Two modifications to insulin-like growth factor 1: a 13-residue extension on the N-terminus (Long) and an arginine substituted at position three (R3). The result is 83 residues against the native 70.
Is IGF-1 LR3 a peptide?
At 83 residues it sits in protein territory, and it is produced recombinantly and not by stepwise synthesis. That changes what its certificate has to report.
Why does a recombinant product need different certificate fields?
Its impurities come from the production system: host cell protein, residual DNA and misfolded or truncated forms. Those have no equivalent in solid-phase synthesis, where impurities are chemical relatives of the target.
Why does endotoxin matter more here?
Bacterial expression systems are a direct source of it, and endotoxin activates immune signalling in cultured cells at very low concentrations. Ordinary sterilisation does not remove it.
Why was the CAS number removed from this listing?
CAS 946870-92-4 passes the check digit but resolves in PubChem to an unrelated ionizable lipid. We removed it instead of leaving a number pointing at the wrong molecule.
Can HPLC purity confirm the protein is folded correctly?
No. Reversed-phase chromatography reports the share of detected peak area that is the target. A correctly sized chain folded wrongly is not something that measurement addresses.
References
- Cascieri, M.A., et al. (1991). Characterization of the biological activity of IGF-I analogs with reduced affinity for IGF binding proteins. Advances in Experimental Medicine and Biology, 293, 23-30.
- Dunaiski, V., Dunshea, F.R., Walton, P.E., & Goddard, C. (1997). Long [R3] insulin-like growth factor-I reduces growth, plasma growth hormone and IGF binding protein-3 in rats. Journal of Endocrinology, 155(3), 559-565.
- Raetz, C.R.H., & Whitfield, C. (2002). Lipopolysaccharide endotoxins. Annual Review of Biochemistry, 71, 635-700.
- Dong, M.W. (2006). Modern HPLC for Practicing Scientists. Wiley.
- Fenn, J.B., Mann, M., Meng, C.K., Wong, S.F., & Whitehouse, C.M. (1989). Electrospray ionization for mass spectrometry of large biomolecules. Science, 246(4926), 64-71.
- Manning, M.C., Chou, D.K., Murphy, B.M., Payne, R.W., & Katayama, D.S. (2010). Stability of protein pharmaceuticals: an update. Pharmaceutical Research, 27(4), 544-575.