IGF-1 DES

1 Identity

Recombinant single-chain protein with three intrachain disulfide bonds. Not a synthetic peptide and not made by solid-phase synthesis. Regulated as a biological product in its full-length form. which is the canonical name. The following are not synonyms, and each is a different article with a different mass: full-length recombinant human IGF-1, which is mecasermin, the active moiety of the approved product Increlex (Ipsen); and IGF-1 LR3.

Sequence

TLCGAELVDALQFVCGDRGFYFNKPTGYGSSSRRAPQTGIVDECCFRSCDLRRLEMYCAPLKPAKSA — residues 4 to 70 of the 70-residue mature human IGF-1 chain, that is the mature chain less the N-terminal tripeptide Gly-Pro-Glu, giving a 67-residue single chain of approximately 7.37 kDa. Free N-terminal amine on threonine, free C-terminal carboxylic acid on alanine. Three intrachain disulfides in the IGF-1 pattern: Cys6-Cys48, Cys18-Cys61 and Cys47-Cys52 in mature numbering, which become Cys3-Cys45, Cys15-Cys58 and Cys44-Cys49 after the truncation. Produced by recombinant expression — most commonly as an E. Coli inclusion body requiring solubilization and oxidative refolding — or by controlled cleavage of full-length recombinant IGF-1. The expression host is A release-critical declaration. What distinguishes correctly folded material from the scrambled-disulfide isomers that co-purify with it is the disulfide connectivity, not the amino acid sequence, and no chemical-synthesis panel detects that difference: a scrambled isomer is exactly isobaric with correctly folded protein.

Molecular formula

C319H495N91O96S7 (oxidized, three disulfides). C319H501N91O96S7 fully reduced, six free thiols.

Average mass

7,365.43 Da for the correctly folded three-disulfide protein (C319H495N91O96S7), arithmetic from the sequence on IUPAC 2021 abridged conventional atomic weights; the older pre-2021 set gives 7,365.35 for the same formula. The fully reduced chain is 7,371.48 Da (C319H501N91O96S7), or 7,371.40 on that older set — exactly 6.05 Da heavier either way, being the six hydrogens lost on forming three disulfides. The arithmetic can be checked against the parent: full-length IGF-1 at 7,648.71 less Gly-Pro-Glu at 283.28 gives 7,365.43, and adding back six hydrogens for three broken disulfides gives 7,371.48. That six-dalton gap is the whole finding on this record, because the number the peptide-seller channel actually publishes is the reduced one: one seller prints 'Molecular Weight 7371.48' on its 1 mg listing of this article, and 7,371 is likewise the figure quoted by several institutional-adjacent suppliers. A supplier quoting 7,371 is quoting a molecule with six free thiols — which is to say a molecule whose three disulfides have not been shown to exist. Both figures are arithmetic from the sequence; on a folded protein the released figure would still be the measured intact mass, never a quoted one.

Monoisotopic mass

7,360.4694 Da for the oxidized three-disulfide protein; 7,366.5164 Da fully reduced. At 7.4 kDa the isotope envelope is resolved only on high-resolution instruments and the routine release measurement is a deconvoluted average mass, so these monoisotopic figures are reference values rather than acceptance criteria.

Salt / variant note

(1) Correctly folded des(1-3)IGF-1, C319H495N91O96S7, 7,365.43 / 7,360.4694. (2) the same chain fully reduced, C319H501N91O96S7, 7,371.48 / 7,366.5164 — and this is a live commercial finding, not a theoretical one: one seller publishes 'Molecular Weight 7371.48' on its 1 mg listing, and 7,371 is the figure the channel repeats. Disulfide connectivity, not amino acid sequence, is the only thing that separates correctly folded material from the scrambled isomers that co-purify with it, so a supplier quoting the reduced mass has quoted a molecule whose folds have not been shown to exist. (3) full-length recombinant human IGF-1, C331H512N94O101S7, 7,648.71 / 7,643.5862, plus 283.28 Da — the active moiety of the approved product Increlex (mecasermin, Ipsen), far more widely produced, and the obvious substitution. (4) IGF-1 LR3, 83 residues, C400H619N111O115S9, 9,111.55 / 9,105.3487, plus 1,746.1 Da — a separate record in this catalog, found at all four tracked sellers, and therefore the variant actually in circulation and the likeliest contents of a vial labeled des. (5) IGF-II, of the 7,469 Da class. (6) human insulin, C257H383N65O77S6, 5,807.63 / 5,803.6376 — the cheap fill for anything sold by the milligram in this class. (7) E. Coli material retaining the initiator methionine, plus 131.04 Da on whichever chain it sits on. (8) any scrambled-disulfide isomer of the correct chain: exactly isobaric with correctly folded material at 7,365.43, invisible to intact mass, invisible to RP-HPLC area percent, and resolvable only by non-reduced peptide mapping. All masses are arithmetic from the stated formulas.

2 Class & testing panel

Form

Single article

Testing panel

P4 — panel definitionA default chemical-synthesis release panel does not fit this article and is not used for it: such a panel carries no host-cell protein test, no residual host-cell DNA test, no disulfide mapping, no aggregate test and no mandatory endotoxin test, and a recombinant three-disulfide protein has none of the failure modes that panel addresses and all of the ones it does not. Nor is this a preparation of undefined composition: the composition is knowable, and is simply unproven on any lot in this channel

3 Primary sources & evidence

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

Published literature exists and is rodent and in vitro, together with an agricultural and cell-culture-reagent literature: truncated and analog IGF-1 proteins are sold as serum-free-medium supplements for mammalian cell culture, which is a genuine and documented laboratory use conducted by suppliers who are set up for it, and one reagent supplier's catalog position reflects exactly that market. No controlled human trial of this specific truncated variant was identified. The attribution rule that governs this record: the human clinical record in this area belongs to full-length recombinant IGF-1, mecasermin, a different and licensed article approved as Increlex, and cannot be read across to a 67-residue truncated variant. That distinction is the main content of the citation index page for this record. No published intact-mass determination on a folded lot of the truncated protein was located either, so the mass figures here are derived rather than measured.

4 Storage & specification

Storage

Lyophilized protein in a sealed vial, stored at -20 degrees C, with -80 degrees C used for long-term hold and for reference material kept for library and comparison purposes; this is not a room-temperature or refrigerated article, and the label states that rather than leaving it to inference. Vials are equilibrated to ambient temperature before opening. Two conditions specific to a refolded three-disulfide protein are carried on the label rather than left to a generic peptide storage rule, which addresses neither: the protein is sensitive to freeze-thaw in solution, so solution is not cycled through repeated freezing, and it is sensitive to surface adsorption at low concentration, which governs the container and the handling of dilute working stock.

Shelf life

Every lot is dated from the date of QA release, carries a printed retest date, and enters the first-expiry-first-out rotation against that printed date rather than against receipt date. No interval is carried across from the synthetic-peptide records, because the attributes that limit this article are the ones a folded protein loses first: disulfide connectivity by non-reduced peptide mapping, aggregate content, deconvoluted intact mass, and the oxidation state of the six cysteines. The interval is set on real-time data at the labeled condition for those attributes across three lots, is shortened on data, and is never extended without a completed dataset. The assignment is reviewed annually and the review is a documented decision with a named owner; supply, cost and demand are not inputs to it.