PEG-MGF

1 Identity

Undefined composition. A polyethylene-glycol conjugate of a synthetic peptide, in which neither the polymer nor the conjugation is specified by any vendor: no declared PEG nominal molecular weight, no declared dispersity, no declared conjugation chemistry and no declared attachment site. Because polyethylene glycol is a polydisperse polymer, the article is a mass envelope of oligomers rather than a compound with a molecular weight. It is not a protein, not a splice variant, and not a defined peptide as sold. and "MGF 24-mer. Loosely and wrongly used for it: "MGF", "mechano growth factor", "IGF-1Ec" and "IGF-1Eb" — not one of which names this conjugate.

Sequence

No defined sequence for the article as sold. The peptide component is given in the trade as the 24-residue IGF-1 Ec E-domain sequence H-Tyr-Gln-Pro-Pro-Ser-Thr-Asn-Lys-Asn-Thr-Lys-Ser-Gln-Arg-Arg-Lys-Gly-Ser-Thr-Phe-Glu-Glu-Arg-Lys-OH (YQPPSTNKNTKSQRRKGSTFEERK), and this company has not verified that assignment against any authenticated reference standard. The conjugate has no sequence in any useful sense: a methoxy-polyethylene glycol chain of undeclared nominal mass and undeclared dispersity is attached by undeclared chemistry to an undeclared site, and with three lysine epsilon-amines plus the N-terminal alpha-amine there are four candidate attachment points — Lys8, Lys11, Lys16 and the N-terminal alpha-amine — that no vendor document in this market distinguishes. A sequence is not an identity when the thing attached to it is not specified.

Molecular formula

Not established, and none can exist for the conjugate. A molecular formula requires a fixed atom count; a polydisperse polymer has none. For the peptide component alone, and stated as such: free acid C121H199N41O40; C-terminal amide C121H200N42O39. The ethylene-oxide repeat unit is C2H4O, 44.053 average and 44.02621 monoisotopic, which is the spacing of the envelope and not a component of a formula.

Average mass

Not established for the conjugate, and no authenticated reference standard exists against which a conjugate mass could be confirmed. The conjugate is a mass envelope of oligomers spaced by the 44.053 Da ethylene-oxide repeat, not a mass. For the peptide component only, on IUPAC 2021 abridged conventional atomic weights: free acid C121H199N41O40 = 2868.170 Da; C-terminal amide C121H200N42O39 = 2867.186 Da. 2868.13 and 2867.14 also circulate for those same two formulas and are those formulas on the pre-2021 atomic-weight table; neither figure is wrong, and this catalog standardizes on the 2021 table and states the basis on the face of every mass, so 2868.170 and 2867.186 are the printed figures with the older-table values recorded as their equivalents. Both formulas reproduce exactly when reconstructed from the 24-mer sequence.

Monoisotopic mass

None for the conjugate; the concept does not apply to a polydisperse polymer, and a certificate reporting a monoisotopic mass for a PEG conjugate has run a small-molecule template against a polymer. For the peptide component only: free acid 2866.47980 Da neutral, [M+H]+ 2867.48708, [M+3H]3+ m/z 956.5005; C-terminal amide 2865.49578 Da neutral, [M+H]+ 2866.50306. Those figures do not move with the atomic-weight table, because nuclide masses do not move.

Salt / variant note

The substitution risk here is not a molecule swapped for a molecule; it is a definition swapped for a definition, and no mass test detects it. (1) the unpegylated 24-mer sold as "MGF", which is the same peptide component without the polymer: free acid 2868.170 / 2866.47980, [M+H]+ 2867.48708. A lot of plain 24-mer shipped as PEG-MGF is undetectable against a specification that never stated a PEG mass, and the plain 24-mer is the cheaper article in the same market. (2) PEG chain length: nominal 2 kDa, 5 kDa, 10 kDa, 20 kDa and 40 kDa mPEG reagents are all in ordinary commerce, they differ from one another by an order of magnitude in mass, and no vendor declares which is used — so two vials bearing the same product name can differ by 38 kDa. (3) conjugation chemistry: succinimidyl-ester acylation to an amine, aldehyde reductive amination, and maleimide to a thiol are three different linkages with three different hydrolytic stabilities, and the sequence contains no cysteine, so a maleimide-conjugated lot has been attached to something the sequence does not contain. (4) attachment site: three lysine epsilon-amines at positions 8, 11 and 16 plus the N-terminal alpha-amine give four candidate points and, in practice, a positional mixture; none is deducible from any mass. (5) degree of conjugation: mono-, di- and tri-PEGylated species and unreacted free peptide coexist in any real conjugation product, and the ratio is a specification attribute nobody publishes. (6) species axis, which is an identity question and not a biology one: the human transcript is IGF-1Ec and the rodent is IGF-1Eb, they yield different E-peptides, and the literature records the mode of action as species-specific at PMID 27838607 and PMID 24776619 — material sold citing rodent work is citing across a documented species barrier. (7) the C-terminal axis on the peptide component: free acid 2868.170 against amide 2867.186, 0.984 Da apart and routinely unstated.

2 Class & testing panel

Form

Single article

Testing panel

P7 — panel definition

3 Primary sources & evidence

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

Published literature exists for the E-domain peptide and none whatever for the pegylated article. The five PubMed records indexed under "PEG-MGF" or "pegylated mechano growth factor" are not studies of PEG-MGF: they concern PEGylated IGF-I conjugates, PEG-rhGH, general IGF-I system reviews, and one 2026 narrative review of performance-enhancing peptides. The pegylated molecule that is actually sold has never been the subject of a published study of any kind: not in vitro, not in animals, not in humans. Identifiers and study types for the surrounding literature, which belongs to other articles: PMID 17156777, in vitro, human myogenic cells; PMID 21354439, in vitro, human muscle progenitor cells; PMID 19567392, human observational with in-vitro characterization; PMID 30062517, human observational; PMID 33222041, human; PMID 27838607 and PMID 24776619, reviews addressing species-specificity of the E-peptide; PMID 25466910, biotechnological production and mass-spectrometric characterization for doping control; PMID 20564425, PMID 23749893, PMID 32772171 and PMID 27931832, human oncology association studies of IGF-1Ec expression; PMID 25678113 and PMID 25606570, animal. No registered human clinical trial of MGF or PEG-MGF was identified. The evidence base grades F. No human safety data exist for PEG-MGF in any form at any exposure: no toxicology package, no pharmacokinetic study, no immunogenicity assessment — and PEG-conjugated synthetic peptide fragments are a recognized immunogenicity risk class. Literature volume by study type is printed at the head of the research page.

4 Storage & specification

Storage

Lyophilized powder at -20 degrees C plus or minus 5 degrees C, desiccated and protected from light, in amber glass with a nitrogen headspace.

Shelf life

No stability-derived retest interval is issued. A conjugate of undeclared polymer mass, dispersity, conjugation chemistry and attachment site presents no stability-indicating attribute to trend, which is the same defect that leaves the release panel without a governing specification. Each container is dated from receipt, and what limits that date is physical rather than chemical: desiccation, an intact nitrogen headspace, closure integrity and protection from light.