IGF-1 LR3

IGF-1 LR3 is a recombinant, engineered analogue of human insulin-like growth factor 1. Native IGF-1 is a 70-amino-acid single-chain protein with three intramolecular disulfide bonds. IGF-1 LR3 is 83 residues long because it carries a 13-residue N-terminal extension retained from the fusion construct used to express it, and it substitutes arginine for glutamic acid at position 3 of the native sequence, which is the origin of the R3 designation. Its approximate mass is 9.1 kDa, roughly 1.5 kDa heavier than native IGF-1. It is supplied as a lyophilized (freeze-dried) recombinant protein for research use only.

The compound is a growth factor analogue rather than a secretagogue, which is the single most important classification point on this page. It does not act on the pituitary to release growth hormone; it is a ligand for the insulin-like growth factor 1 receptor. The engineered changes were introduced to lower affinity for the insulin-like growth factor binding proteins, the carrier proteins that sequester IGF-1 in serum and in serum-containing culture media. IGF-1 LR3 has no approved indication in any jurisdiction, is widely used as a cell-culture supplement in bioprocessing literature, and is a prohibited substance in sport.

The parent molecule was sequenced by Rinderknecht and Humbel in 1978, who reported the 70-residue IGF-1 chain and its homology with proinsulin (PubMed 632300). The engineered analogues came out of fusion-protein expression work in Adelaide, which left a defined N-terminal extension on the recombinant product.

Francis and colleagues described the recombinant fusion analogue series in 1992, separating binding-protein affinity from receptor affinity as contributors to potency (PubMed 1378742). Tomas and colleagues reported that IGF-1 variants were anabolic in dexamethasone-treated rats (PubMed 1371669). Ballard and colleagues later reviewed the truncated analogue des(1-3)IGF-I (PubMed 8930132).

The evidence base is substantial for receptor biology and cell-culture performance and thin beyond that: a large industrial literature on IGF-1 LR3 as a serum-free media component, a modest 1990s rodent literature, and no modern development programme.

The literature describes IGF-1 LR3 as binding the insulin-like growth factor 1 receptor, a receptor tyrosine kinase. Reported downstream events include receptor autophosphorylation, recruitment of insulin receptor substrate proteins and activation of the PI3K/Akt and MAPK cascades. Cross-reactivity with the insulin receptor is reported at lower affinity.

The useful distinction is receptor class. GHRP-6, hexarelin, ipamorelin and MK-677 act at the ghrelin receptor; sermorelin, tesamorelin, CJC-1295 and Mod GRF 1-29 act at the GHRH receptor. Both are secretagogue families acting on the pituitary, while IGF-1 LR3 bypasses that axis and engages a growth factor receptor directly.

A methodology caveat is central. Apparent potency depends heavily on the binding-protein content of the assay system, so results from serum-free media, serum-containing media and whole-animal models are not interchangeable. Quantities belong to each publication’s own methodology.

Sealed lyophilized IGF-1 LR3 is stored frozen, conventionally at -20°C or lower, shielded from light, with repeated freeze-thaw cycles avoided. No duration is stated here: the stability window is documented on the batch Certificate of Analysis.

Recombinant proteins of this size have degradation routes short peptides do not. Aggregation, deamidation and scrambling of the three disulfide bonds are the described failure modes, and any of them can change activity without changing appearance.

Reconstitution is the term for returning a lyophilized protein to solution; this page defines the term and gives no procedure. IGF-1 LR3 belongs to the aqueous-soluble class, and a correctly folded protein is more solubility-sensitive than a short peptide. Preparation parameters belong to the published methodology being reproduced.

Lyophilized protein is hygroscopic, meaning it takes up atmospheric moisture, and is best handled in low humidity with minimal open-container exposure. Lot numbers are recorded against experimental data so identity questions trace back to the right batch.

Identity for a recombinant protein is established differently from a synthetic peptide. Reversed-phase HPLC, size-exclusion chromatography, SDS-PAGE and mass spectrometry are the usual methods, with an observed mass near 9.1 kDa as the primary check. Verified purity is documented per lot on the Certificate of Analysis, which also identifies any carrier protein or excipient.

Because the material is expressed in a host organism, host-cell protein content, endotoxin level and monomer rather than aggregate content are meaningful specifications. Catalyst Compounds material is batch tested with a published Certificate of Analysis.

IGF-1 LR3 is read against both the IGF family and the secretagogues it is often filed with.

• Sermorelin and Tesamorelin.
  GHRH-receptor analogues acting on the pituitary, upstream of a growth factor receptor ligand.
• CJC-1295 and Mod GRF 1-29.
  Further GHRH-receptor compounds, useful as class controls in receptor-specificity experiments.
• GHRP-6 and Hexarelin.
  Ghrelin receptor hexapeptides, a third receptor class, neither of which binds the IGF-1 receptor.
• MK-677.
  A non-peptide ghrelin receptor research compound, completing the receptor-class contrast.

Rinderknecht E, Humbel RE. (1978). The amino acid sequence of human insulin-like growth factor I and its structural homology with proinsulin. J Biol Chem.
PubMed 632300

Francis GL, Ross M, et al. (1992). Novel recombinant fusion protein analogues of insulin-like growth factor (IGF)-I indicate the relative importance of IGF-binding protein and receptor binding for enhanced biological potency. J Mol Endocrinol.
PubMed 1378742

Tomas FM, Knowles SE, et al. (1992). Insulin-like growth factor-I (IGF-I) and especially IGF-I variants are anabolic in dexamethasone-treated rats. Biochem J.
PubMed 1371669

Ballard FJ, Wallace JC, et al. (1996). Des(1-3)IGF-I: a truncated form of insulin-like growth factor-I. Int J Biochem Cell Biol.
PubMed 8930132

IGF-1 LR3 is stocked in one format only, lyophilized powder in sealed single-compound vials at 1mg per vial, across one house brand and two supplier brands. No capsule or liquid spray listing exists for this compound. Per-vial strength is a specification, and each lot carries a published Certificate of Analysis.

• Browse all IGF-1 LR3 research products
• Catalyst Compounds IGF-1 LR3, 1mg vial
• Real Peptides IGF-1 LR3, 1mg vial
• Groov Bioscience IGF-1 LR3, 1mg vial
• Collections: Research Vials. Documentation: COA and Lab Testing.

These products are sold for Research Use Only and are not intended for human consumption.