01 / Comparison
IGF-1 LR3 and IGF-I, side by side.
IGF-1 LR3 is the 70-residue human IGF-I chain with two changes: 13 residues added before its N-terminus, and arginine in place of glutamate at position 3 of the IGF-I region. That makes 83 residues in all. Both chains have the same three disulfide bonds, numbered 13 positions higher in LR3.
| IGF-1 LR3 | Human IGF-I | |
|---|---|---|
| Length | 83 residues | 70 residues |
| N-terminal extension | 13 residues, MFPAMPLSSLFVN | None |
| Position 3 of the IGF-I region | Arg | Glu |
| Disulfide bonds | Cys19–Cys61, Cys31–Cys74, Cys60–Cys65 | Cys6–Cys48, Cys18–Cys61, Cys47–Cys52 |
| Sequence | MFPAMPLSSL FVNGPRTLCG AELVDALQFV CGDRGFYFNK PTGYGSSSRR APQTGIVDEC CFRSCDLRRL EMYCAPLKPA KSA | GPETLCGAEL VDALQFVCGD RGFYFNKPTG YGSSSRRAPQ TGIVDECCFR SCDLRRLEMY CAPLKPAKSA |
| Public record | FDA GSRS, UNII M9L22Y19H9; CAS 143045-27-6 | UniProt P05019, chain 49–118 |
02 / Molecular architecture
A closer look at the chain.
The design adds a 13-residue N-terminal extension and replaces glutamate with arginine at position 3 of the IGF-I region. The position refers to that region, not the third residue of the extended molecule.
- IGF-I analog
- 13-residue extension
- Arg3 substitution
Reference information: [1][2][3]. Actual lot identity must be verified separately.
Two edits with separate numbering.
Long Arg3 IGF-I combines an N-terminal extension with an arginine substitution at position 3 of the IGF-I region. The extension and the substitution are separate design features. If a sequence is numbered from the start of the extended molecule, its third residue is not what the Arg3 name refers to.
Receptor binding versus binding proteins.
The analog study considered both receptors and IGF-binding proteins. These are distinct interactions: a binding-protein measurement is not a direct measurement of receptor signaling. Their separate roles help explain why cellular comparisons can depend on which proteins and conditions are present in the experimental system.
Structure and research references: [1]
03 / Read the evidence
Research & analytical context.
The original analog study compared receptor binding, IGF-binding-protein interactions and cellular activity. Differences in binding-protein affinity helped explain why activity varied between the tested cell systems.
Read the references: [1][2][3].
The distinction that matters
Lower affinity for a binding protein does not mean greater activity in every model. Distinguish LR3 from native IGF-I and other truncated or extended analogs when selecting reference data.
04 / From reference to record
Know the lot, too.
A publication describes its own test material. Your lot’s certificate describes what was tested on that lot. Keep the compound name, batch number and reported methods together when reviewing a result.
Identity & composition
Check sequence or chemical form, terminal modifications, counterion and—where relevant—each blend component.
Analytical results
Read purity, content, sterility and endotoxin results as separate measurements. Only call a test passed when the actual report supports it.
Handling & storage notes
Lyophilized material: Store at −20°C; protect from light and moisture.
Follow the material-specific label and supporting storage documentation. These temperatures do not establish a shelf life.
How to store lyophilized peptides05 / Reference questions
A few details, explained.
What does LR3 identify in the name?
It refers to the Long Arg3 analog: an extended chain carrying the Arg3 substitution in the IGF-I region. It does not refer to a vial size or a three-component formulation.
Does weaker binding to an IGF-binding protein mean stronger receptor binding?
No. They are different measurements involving different binding partners. One cannot be used as a numerical substitute for the other without the corresponding experimental data.
Read alongside the references: [1]
06 / Continue reading
Go to the source.
Each source is labeled by its type. External sources are not Pioneer batch certificates.
- Recombinant IGF-I analogs: receptor and binding-protein study (1992)Published research · Read source (opens a new tab)
- FDA GSRS · IGF-1 LR3 substance record, UNII M9L22Y19H9Public record · Read source (opens a new tab)
- UniProt · Insulin-like growth factor I record, P05019; IGF-I is chain 49–118Public record · Read source (opens a new tab)