IGF-1 LR3

1 Identity

One name is used for five circulating molecules, and this record keeps them apart, because they are separated by mass, by chain length, and in one case by a single character in a sequence label: Long R3 IGF-1 (LR3) — 83 residues; C400H619N111O115S9; average mass 9,111.55 Da; monoisotopic 9,105.3487 Da. The fully reduced 83-mer — C400H625N111O115S9; average 9,117.60 Da; monoisotopic 9,111.3957 Da. This is failed refolding, not a distinct product. R3 IGF-1 — 70 residues; C332H517N97O99S7; average 7,675.79 Da; monoisotopic 7,670.6448 Da. It differs from LR3 by one character in the name and by 1,435.8 Da in mass. Mecasermin (wild-type mature human IGF-1) — 70 residues; C331H512N94O101S7; average 7,648.71 Da; monoisotopic 7,643.5862 Da; 27.07 Da from R3. Des(1-3)IGF-1 — 67 residues; C319H495N91O96S7; average 7,365.43 Da; monoisotopic 7,360.4694 Da.

Sequence

Recombinant, refolded, three-disulfide single-chain protein produced by bacterial expression. It is not a synthetic peptide and no part of it is made by solid-phase synthesis. The chain is recovered from E. Coli inclusion bodies. An 83-residue single chain with three intramolecular disulfides. One-letter: MFPAMPLSSLFVN-GPRTLCGAELVDALQFVCGDRGFYFNKPTGYGSSSRRAPQTGIVDECCFRSCDLRRLEMYCAPLKPAKSA. A 13-residue N-terminal leader (Met-Phe-Pro-Ala-Met-Pro-Leu-Ser-Ser-Leu-Phe-Val-Asn), derived from methionyl porcine growth hormone, is fused to mature human IGF-1(1-70) carrying the Glu3Arg substitution — the mature segment begins GPR-, not GPE-. A free N-terminal alpha-amine; a free C-terminal carboxylic acid; no amidation; no synthesis end-caps. Six cysteines, three disulfides: Cys19-Cys61, Cys60-Cys65 and Cys31-Cys74 in 83-residue numbering, corresponding to Cys6-Cys48, Cys47-Cys52 and Cys18-Cys61 in mature IGF-1 numbering (shifted +13 by the leader). What distinguishes correctly folded material from the scrambled-disulfide isomers that co-purify with it is the disulfide connectivity, not the sequence: scrambled isomers are exactly isobaric and frequently co-elute on reversed phase.

Molecular formula

Oxidized, three disulfides formed: C400H619N111O115S9. Fully reduced, six free thiols: C400H625N111O115S9.

Average mass

Oxidized, 9,111.55 Da computed on IUPAC 2021 abridged conventional atomic weights; the older pre-2021 set yields 9,111.45 Da. Fully reduced, 9,117.60 Da on the 2021 set and 9,117.50 Da on the older set — a +6.05 Da gap on reduction, and that gap is the arithmetic that proves the three disulfides are formed.

Monoisotopic mass

9,105.3487 Da oxidized (C400H619N111O115S9); 9,111.3957 Da fully reduced (C400H625N111O115S9). Monoisotopic is not the practical release measurement at 9 kDa: the monoisotopic peak is not the base peak of the isotope envelope at that mass, so a usable certificate reports a deconvoluted average mass from a multiply-charged ESI envelope with the charge-state series printed. These figures are reference values, not acceptance criteria.

Salt / variant note

His-tagged constructs add roughly 840 Da (a His6 tag plus linker) and are often shipped unlabeled. Scrambled-disulfide isomers remain isobaric and undetectable by mass alone; only non-reduced peptide mapping can identify them.

2 Class & testing panel

Form

Single article

Testing panel

P4 — panel definition

3 Primary sources & evidence

The index reports the design and provenance of the literature, not a conclusion about effect.

Several hundred primary in-vitro and animal-science reports exist, the majority of them cell-culture and livestock growth studies in which the analogue is used as a serum-free media supplement. It has been a catalog reagent of established life-science suppliers for roughly three decades, which is why the literature is large in volume and methodological rather than clinical in character. Controlled human clinical data exist only for recombinant human IGF-1, mecasermin — a different 70-residue molecule with its own approved US product and its own label — and that dataset cannot be read across to an 83-residue analogue carrying a foreign N-terminal leader and a point substitution. A separate analytical literature exists on doping-control detection methods for the analogue, which is itself a fact about who has been studying it and why. Citation index entries for this record are limited to the cell-culture, animal-science and analytical-detection literature, with an explicit note that no human interventional dataset exists for this construct.

4 Storage & specification

Storage

A refolded 9 kDa three-disulfide protein, held lyophilized at -20 degrees C plus or minus 5 degrees C for routine stock and at -80 degrees C for long-term retention, desiccated and protected from light. Freeze-thaw cycling is controlled as A named parameter, because aggregation rather than chemical degradation is the governing failure mode, and low-concentration solutions are handled in low-binding labware, because surface adsorption is a real loss mechanism at these concentrations. None of those controls appears in a peptide storage rule: this article is a refolded protein and is held on protein conditions rather than on peptide ones. Reference material held for library or comparison purposes is kept at -80 degrees C, physically segregated from routine stock.

Shelf life

Dated from QA release, with a printed retest date on every unit and first-expiry-first-out enforced against that date. The interval is set on this company's own real-time and accelerated data rather than inherited from a supplier's certificate. The retest-limiting attributes are physical rather than chemical: aggregation, and the scrambled-disulfide isomers, which are isobaric with correctly folded material and are therefore trended by non-reduced peptide mapping rather than by mass. Deconvoluted average mass from a multiply-charged ESI envelope with the charge-state series printed, water content, and the +6.05 Da reduced-minus-oxidized gap that demonstrates three formed disulfides are trended alongside them.