IGF-1 LR3 (Long R3 insulin-like growth factor-1) is a synthetic analogue of human IGF-1 engineered specifically for cell-culture work. Two modifications define it: an arginine substituted for glutamic acid at position 3 of the native sequence, and a 13-residue extension peptide at the N-terminus — together the “Long” and “R3” of the name, producing an 83-amino-acid protein. Both changes serve one research purpose: native IGF-1 in biological media is captured by IGF-binding proteins, which sequester it and complicate dose-response work; the LR3 modifications drastically reduce binding-protein affinity while preserving receptor activity, so more of what is added to a culture stays free.
Research background
IGF-1 signalling is one of the most studied axes in cell biology — growth, differentiation, and metabolism all run partly through the IGF-1 receptor — and cell-culture experiments in that literature need a ligand whose free concentration is predictable. That is the niche LR3 was built for, and it has become a standard media supplement in research bioprocessing for exactly that reason. It is worth being precise about what LR3 is not: it is not natural IGF-1, and its binding-protein escape makes its behaviour in any system quantitatively different from the native molecule — which is the designed-in property, not a side effect.
Structure and analytical profile
IGF-1 LR3 is an 83-residue single-chain protein, molecular weight approximately 9,110 g/mol — an order of magnitude above most peptides in this catalog, closer to a small protein than a synthetic peptide. It contains three intramolecular disulfide bridges, and correct folding matters analytically: mass spectrometry establishes identity, and chromatographic methods resolve misfolded or aggregated species, which are the characteristic impurities of recombinant production.
Verifying a lot
Lot number matching the vial, a named issuing laboratory with the original report attached, and a report verifiable at the source. Every IGF-1 LR3 lot we sell publishes its certificate in the certificate archive.
Handling notes
Supplied lyophilized; store cool, dark and dry. As a folded protein it is less forgiving than short peptides — avoid repeated freeze-thaw of reconstituted material and vigorous agitation, which promote aggregation. For qualified laboratory settings only.
Frequently asked research questions
How does LR3 differ from native IGF-1? An Arg-for-Glu substitution at position 3 plus a 13-residue N-terminal extension. The effect is sharply reduced affinity for IGF-binding proteins with preserved receptor activity — a cell-culture engineering choice.
Is it a peptide or a protein? At 83 residues with three disulfide bridges it is best described as a small protein, and its handling and analytics follow protein rules rather than short-peptide rules.
What should its certificate show? Identity by mass spectrometry consistent with ~9,110 g/mol, chromatographic purity resolving aggregates and misfolds, lot number, issuing laboratory, report date.
All products discussed are for laboratory research use only and are not for human or veterinary consumption. Nothing here describes or endorses any use in humans or animals.