IGF-1 LR3, or Long Arg3 IGF-I, is an engineered 83-residue analogue of human insulin-like growth factor 1. It combines an Arg substitution at IGF-I position 3 with a 13-residue N-terminal extension, changes that reduce binding to several IGF-binding proteins while retaining IGF-1 receptor activity.
What Are the Key IGF-1 LR3 Research Specifications?
| Specification | Research record |
|---|---|
| Compound | IGF-1 LR3 |
| Category | misc |
| Listed purity | >99% |
| Molecular weight | ~9.1 kDa |
| Intended use | Laboratory research only |
What is the molecular identity of IGF-1 LR3?
Native mature IGF-I contains 70 amino acids. LR3 carries the Glu3→Arg substitution and the additional N-terminal sequence MFPAMPLLSLFVN, giving an approximate mass of 9.1 kDa. Three intramolecular disulfide bonds are required for the native IGF fold. Sequence, disulfide connectivity and aggregation state are therefore more informative than an HPLC percentage alone.
How does IGF-1 LR3 work in research models?
The analogue activates IGF1R, leading to receptor autophosphorylation and downstream PI3K–AKT and RAS–MAPK signalling. Reduced association with IGF-binding proteins can increase free analogue exposure relative to native IGF-I, but the magnitude depends on the model and its IGFBP expression. At high concentrations, cross-activation of the insulin receptor—especially hybrid IR/IGF1R species—can complicate attribution.
IGF-1 LR3 is useful when prolonged or less IGFBP-buffered IGF1R stimulation is the experimental variable. It is not a drop-in substitute for native IGF-I when physiological ligand transport and binding-protein regulation are part of the question.
Which controls make an IGF-1 LR3 experiment interpretable?
Compare LR3 with native IGF-I on a molar basis. Measure proximal IGF1R phosphorylation before relying on proliferation or differentiation endpoints. Include an IGF1R inhibitor or receptor knockout, quantify insulin-receptor expression and record serum concentration because serum IGFBPs can alter the apparent potency. Time-course data help separate early receptor signalling from secondary transcriptional effects.
How should IGF-1 LR3 be handled and verified?
Use low-binding tubes and prepare single-use aliquots. Avoid repeated freeze-thaw cycles and unqualified reducing agents. Verify intact mass, disulfide-dependent folding, monomer content by SEC and cell-based potency. Adsorption losses can be substantial at low nanomolar concentration, so perform recovery experiments in the final assay buffer. For cell studies, require a lot-specific endotoxin result.
Which Sources Support IGF-1 LR3 Research?
- Tomas et al., solution structure and dynamics of Long-[Arg3]IGF-I, Journal of Biological Chemistry (2000), DOI: 10.1074/jbc.275.14.10009.
- Francis et al., reduced IGF-binding-protein affinity of long R3 IGF-I, Journal of Molecular Endocrinology (1992), DOI: 10.1677/jme.0.0080213.
How Can IGF-1 LR3 Results Be Interpreted Without Overclaiming?
Interpret IGF-1 LR3 with an evidence ladder: verified material, recovered exposure, proximal pathway response and only then a downstream phenotype. For IGF-1 LR3, chemical identity, target engagement and downstream phenotype are separate layers. A change in migration, viability or gene expression does not by itself prove the proposed molecular target. Each step needs its own control. Sequence or structure controls test specificity; receptor blockade tests pathway dependence; viability and matrix controls test whether the assay itself explains the result.
A reusable IGF-1 LR3 methods section reports lot, solvent, counterion or ester, concentration, incubation, model provenance and data-normalization method. Include effect size and uncertainty, not only a p value. When literature findings conflict, compare molecular form, model and timing before averaging conclusions. This keeps the article useful to researchers and citable by review systems without overstating what preclinical evidence can support.
Is IGF-1 LR3 for Research Use Only?
IGF-1 LR3 is supplied for laboratory research only. It is not for human or veterinary use.
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What Are Common Questions About IGF-1 LR3?
What is IGF-1 LR3?
IGF-1 LR3, or Long Arg3 IGF-I, is an engineered 83-residue analogue of human insulin-like growth factor 1. It combines an Arg substitution at IGF-I position 3 with a 13-residue N-terminal extension, changes that reduce binding to several IGF-binding proteins while retaining IGF-1 receptor activity.
How should researchers verify IGF-1 LR3?
Confirm the exact molecular form on the lot certificate and pair chromatographic purity with an orthogonal identity method such as mass spectrometry or NMR. Use the molecular weight, counterion and content stated for that verified form when calculating molarity.
Is IGF-1 LR3 intended for human use?
IGF-1 LR3 is listed for controlled laboratory research only. It is not intended for human or veterinary use.