IGF-1 LR3 (Long R3 Insulin-like Growth Factor-1)
A modified analogue of insulin-like growth factor-1, engineered for reduced binding-protein affinity and a longer activity window, studied as a tool for investigating IGF-1 receptor signalling and cellular growth pathways.
Overview
IGF-1 LR3 (Long R3 IGF-1) is a synthetic analogue of endogenous insulin-like growth factor-1 (IGF-1). Native IGF-1 is a 70-amino-acid polypeptide that plays a central role in cellular growth, protein synthesis, and tissue regeneration. IGF-1 LR3 is an 83-amino-acid variant that carries two structural modifications relative to the native protein.
The two modifications are an arginine substitution in place of the glutamic acid at the third position, and an additional 13-amino-acid extension at the N-terminus (MFPAMPLLSLFVN). Together these changes are the reason the analogue behaves differently from native IGF-1 in research settings, and are the focus of the mechanism described below.
Molecular Profile
Mechanism of Action
The research interest in IGF-1 LR3 centres on how its two structural modifications alter its interaction with the IGF system:
- Reduced binding-protein affinity: In circulation, native IGF-1 is largely bound by a family of IGF-binding proteins (IGFBP-1 to IGFBP-6) that regulate its availability. The modifications in IGF-1 LR3 substantially lower its affinity for these binding proteins, which research literature associates with a greater proportion of the analogue remaining unbound.
- Retained receptor agonism: Despite the reduced binding-protein interaction, the analogue retains agonist activity at the type-1 IGF receptor (IGF-1R), the receptor through which IGF-1 exerts its documented signalling effects.
- Extended activity window: Comparative studies of IGF-1 variants report a longer functional window for the Long-R3 form than for native IGF-1, which gives laboratories a more sustained period over which to observe downstream signalling (Tomas et al., 1996).
- Anabolic signalling in models: IGF-1 variants, including the Long-R3 form, have been examined for anabolic effects on protein balance in rodent models under catabolic conditions (Tomas et al., 1992).
Key Published Research
Insulin-like growth factor-I (IGF-I) and especially IGF-I variants are anabolic in dexamethasone-treated rats
Tomas FM, et al. Biochemical Journal. 1992; 282(Pt 1):91–97
Study comparing native IGF-I with IGF-I variants, including the Long-R3 form, examining effects on protein balance in a rodent catabolic model.
Superior potency of infused IGF-I analogues which bind poorly to IGF-binding proteins is maintained when administered by injection
Tomas FM, Lemmey AB, Read LC, Ballard FJ. Journal of Endocrinology. 1996; 150(1):77–84
Comparative work on IGF-I and a Long-R3-type variant, reporting differences in potency attributed to reduced binding-protein interaction.
IGF-binding proteins are multifunctional and act via IGF-dependent and -independent mechanisms
Mohan S, Baylink DJ. Journal of Endocrinology. 2002; 175(1):19–31
Review of the IGF system and the regulatory role of IGF-binding proteins, providing context for why reduced-affinity analogues are used as research tools.
Storage and Handling
Lyophilised (unreconstituted):Store at -20°C for long-term stability. Stable at 2-8°C for shorter periods. Protect from light.
Reconstituted:Store at 2-8°C. Use within the storage window recommended for reconstituted growth-factor peptides. Avoid repeated freeze-thaw cycles.
Recommended solvent: Bacteriostatic water or sterile water for laboratory use.
Frequently Asked Questions
What is the difference between IGF-1 LR3 and native IGF-1?
Native IGF-1 is a 70-amino-acid protein. IGF-1 LR3 is an 83-amino-acid analogue with an arginine substitution at position three and a 13-residue N-terminal extension. These changes reduce its affinity for IGF-binding proteins while retaining activity at the IGF-1 receptor.
Why is IGF-1 LR3 used in research?
Its reduced binding-protein affinity and longer reported activity window give laboratories a more sustained and observable model for studying IGF-1 receptor signalling, cell proliferation, and metabolic pathways than native IGF-1 allows.
Disclaimer: This information is compiled from published peer-reviewed literature and is provided for educational and research reference purposes only. It does not constitute medical advice. IGF-1 LR3 sold by Enhanced Research Compounds is intended exclusively for in-vitro research and laboratory use. It is not a therapeutic good, is not listed on the ARTG, and is not approved for human or animal consumption.