IGF-1 LR3: Research Reference

IGF-1 LR3 (Long R3 IGF-I) is a recombinant 83-residue analogue of human insulin-like growth factor I, made in bacteria and folded into shape by three disulfide bridges. It carries arginine in place of glutamic acid at IGF-I position 3 and a 13-residue extension at the front, two changes that let it escape the binding proteins that normally hold IGF-I inactive. Unlike the short peptides in this series, it is a small folded protein, and that changes how it is stored and handled.

This reference collects what a laboratory needs to know about IGF-1 LR3 as a material: how a folded protein behaves in the vial, what it dissolves in, how it is handled at the bench and what to do when an order arrives. Each section below has its own page.

Molecular reference

Name	IGF-1 LR3 (Long R3 IGF-I)
Also known as	LR3IGF-I, Long [Arg3]-IGF-I, LongR3 IGF-I
Structure	Met-Phe-Pro-Ala-Met-Pro-Leu-Ser-Ser-Leu-Phe-Val-Asn extension, then human IGF-I (70 residues) with Arg at IGF-I position 3
Sequence	MFPAMPLSSLFVNGPRTLCGAELVDALQFVCGDRGFYFNKPTGYGSSSRRAPQTGIVDECCFRSCDLRRLEMYCAPLKPAKSA
Residues	83
Disulfide bonds	3 (IGF-I pairing 6-48, 18-61, 47-52)
Molecular formula	C400H619N111O115S9 (our calculation from the sequence)
Molecular weight	About 9.1 kDa (9,111.6 g/mol by our calculation)
Source	Recombinant, expressed in E. coli

The sequence, the 83-residue length, the 9.1 kDa weight and the E. coli source are from the OriGene data sheet for Long R3 IGF-I (AR31185PU-S); the MedChemExpress sheet (HY-P70783) describes the same construct as IGF-I with the 13-residue extension MFPAMPLSSLFVN. PubChem has no record for this protein, so the formula and exact weight are our calculation from the sequence with three disulfide bonds; it matches the 9,111.5 g/mol on our product page. The IGF-I disulfide pairing is from Miller et al., Biochemistry, 1993. Neither supplier sheet gives a CAS number.

Three features of that structure explain most of its behaviour. Its shape depends on three disulfide bridges, and IGF-I is known to fold into two disulfide arrangements of similar stability, the native one and a swapped one (Miller et al., 1993). It carries three methionines, one of them matching methionine 59 of human IGF-I, whose oxidation formulation studies found was driven by light, oxygen and storage temperature (Fransson et al., Pharmaceutical Research, 1996; Fransson, Journal of Pharmaceutical Sciences, 1997). And its extension joins IGF-I through an Asn-Gly bond, the same bond the developers used as a chemically cleavable link when making IGF-I (King et al., Journal of Molecular Endocrinology, 1992). Light, air, agitation and time in solution are therefore the things to manage.

What it is studied for

IGF-1 LR3 was built in Adelaide as a research tool for separating the effects of IGF-binding proteins from those of the receptor. The developers found that its hydrophobic extension, taken from porcine growth hormone, helped the reduced chain fold correctly; in cell lines that secrete binding proteins, Long [Arg3]-IGF-I ranked among the most potent analogues tested (Francis et al., Journal of Molecular Endocrinology, 1992). Its affinity for IGFBP-3, IGFBP-4 and rat plasma binding proteins is roughly 1,000-fold lower than that of IGF-I, giving it 5 to 10 times the potency in cultured L6 myoblasts, and it is cleared from rat plasma much faster (Ballard et al., Growth Regulation, 1993).

In animal research it was about 2.5-fold more potent than IGF-I at partly reversing a steroid-induced catabolic state in rats, even though it binds the type 1 IGF receptor 3-fold less well (Tomas et al., Biochemical Journal, 1992), and over three days it increased small and large intestine weight and crypt size in rats where IGF-I did not (Steeb et al., Gut, 1995). Outside animal work it is a standard cell-culture growth factor; in serum-free Chinese hamster ovary cultures it sustained viability better than insulin (Morris and Schmid, Biotechnology Progress, 2000). The published work on IGF-1 LR3 itself is laboratory and animal research.

Our summaries are in what is IGF-1 LR3 and IGF-1 LR3 research: what the studies actually show.

Stability

As a folded protein, IGF-1 LR3 can change in ways a short peptide cannot: methionine oxidation, disulfide scrambling, aggregation when shaken and loss to surfaces when dilute. Supplier figures for the refrigerated solution are shorter than for most peptides. The IGF-1 LR3 stability page covers each route and what visible changes mean.

Solubility

IGF-1 LR3 carries a net positive charge at near-neutral pH, and both supplier sheets reconstitute it in water. The IGF-1 LR3 solubility guide explains the supplier concentration range, why phosphate buffers are avoided for storage and what causes haze.

Handling

Bench practice for IGF-1 LR3 is about keeping a small amount of protein cold, dark, still and concentrated enough. The IGF-1 LR3 handling page lists the steps and the common mistakes.

On arrival

What a 1 mg vial should look like, why it travels without an ice pack and where it goes first are on the IGF-1 LR3 on-arrival page.

Storage and reconstitution

Fridge and freezer windows, before and after mixing, are on how long IGF-1 LR3 lasts. Water volumes and the concentration table for a 1 mg vial are on how much bacteriostatic water for an IGF-1 LR3 1 mg vial.

FAQ

Short answers to the questions researchers ask most about storing, mixing and handling IGF-1 LR3 are on the IGF-1 LR3 FAQ.

Where to get it

Vistara Labs supplies IGF-1 LR3 1 mg as a lyophilised vial for laboratory research, shipped within Canada by Canada Post Xpresspost. More detail on sourcing is in Buy IGF-1 LR3 in Canada, and certificates are on our lab reports page. For compounds that act further up the growth hormone axis, see the tesamorelin and CJC-1295 research references.