MGF (Mechano Growth Factor)

1 Identity

IGF-axis peptides and growth-hormone-derived fragments. A plain linear synthetic 24-residue peptide; made by solid-phase synthesis, not derived from tissue. and the C-terminal segment of the E-domain of the human IGF-1Ec splice variant. Not synonyms, and each a different article: IGF-1Eb, the rodent ortholog, which carries a different C-terminal sequence and is sold under the same three letters; and PEG-MGF, which is a separate record in the catalog and a different molecule.

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; one-letter YQPPSTNKNTKSQRRKGSTFEERK, 24 residues, free acid. All-L, entirely proteinogenic. Free N-terminal alpha-amine, free C-terminal carboxylic acid. No acetylation, no amidation, no acylation, no PEG, no D-residue, no non-proteinogenic residue, no cysteine and therefore no disulfide in the 24-mer — which is the compositional fact that separates it from the 25-mer article traded under the same name. The sequence contains no methionine, no cysteine and no tryptophan, so oxidation is not a governing degradation route for it and the absence of an oxidation panel on a certificate for this article is correct rather than an omission. Strongly basic: three Arg, three Lys and a free N-terminus, so it is normally isolated as the trifluoroacetate salt and the counterion is a first-order quantity. The sequence corresponds to the C-terminal segment of the E-domain of human IGF-1Ec, the splice variant generated by a 49-base-pair insertion in exon 5 that shifts the reading frame and produces a distinct C-terminus. Suppliers differ on the exact boundary of the traded 24-mer, so the sequence is confirmed against the incoming supplier's own written specification before any mass tolerance is issued.

Molecular formula

C121H199N41O40 (free acid, salt-free, the 24-mer as written). The 25-residue Cys-extended form C124H204N42O41S. Deletion sequences across the basic stretch: des-Arg C115H187N37O39; des-Lys C115H187N39O39.

Average mass

2,868.17 Da (C121H199N41O40), from the formula on IUPAC 2021 abridged conventional atomic weights: 2,868.170. One institutional supplier prints 2868.16 and the computed value reconciles to 0.01 Da. A rounded 2868.2 also circulates for this peptide and is the same number rounded, not a third value. Comparators: 25-mer Cys-extended form 2,971.31 (+103.14, one cysteine residue, and it imports a sulfur atom the 24-mer does not have); des-Arg deletion 2,711.98 (-156.19); des-Lys deletion 2,740.00 (-128.18). Counterion: on a peptide with seven basic sites a trifluoroacetate lot typically carries 8 to 12 percent w/w counterion, so a nominal 5 mg vial is 4.4 to 4.6 mg of peptide.

Monoisotopic mass

2,866.47980 Da neutral (C121H199N41O40). Working ions for a release measurement: [M+3H]3+ m/z 956.50054; [M+4H]4+ m/z 717.62723; [M+2H]2+ m/z 1,434.24718. Comparators: 25-mer Cys form 2,969.48898 (+103.009 monoisotopic); des-Arg 2,710.37869 (-156.101); des-Lys 2,738.38484 (-128.095).

Salt / variant note

This name carries A genuine two-molecule commercial split and it is measurable by arithmetic. (1) The 24-mer free acid, C121H199N41O40, 2,868.17 average / 2,866.47980 monoisotopic. (2) the 25-mer with an appended C-terminal cysteine, YQPPSTNKNTKSQRRKGSTFEERKC, C124H204N42O41S, 2,971.31 / 2,969.48898 — sold as plain "MGF" by one seller, whose listing prints that sequence. The two differ by +103.14 Da and by one sulfur atom; the appended cysteine exists to provide a PEGylation handle. A buyer specifying "MGF" and receiving either has received a conforming article under the name and a non-conforming article under any real specification. Worth recording separately: that seller's own page prints "MW 2971.99" beside the 25-residue sequence, and the sequence it prints computes to 2,971.31 — a 0.68 Da internal inconsistency on a single listing, which is a smaller version of the same failure the PEG-MGF listing below shows at kilodalton scale. Both failures are recorded, because a catalog that checks certificates by arithmetic must record the small ones as well as the spectacular ones. (3) PEG-MGF, a separate record in the catalog: a PEG-succinimidyl group prefixed to the 25-mer Cys form, polydisperse, presenting as a mass envelope with 44.026 Da spacing rather than as a single accurate mass. Another seller's PEG-MGF page is the worked example of an incoherent certificate — it prints formula C426H682N112O119S11, which computes to about 9,629 Da average, alongside a stated "molecular weight 2867.2 g/mol", a 6.8 kDa internal contradiction on one page. (4) deletion sequences across the Arg14-Arg15-Lys16 stretch where Fmoc couplings cluster and fail: des-Arg C115H187N37O39, 2,711.98 / 2,710.37869 (-156.10 monoisotopic); des-Lys C115H187N39O39, 2,740.00 / 2,738.38484 (-128.09 monoisotopic). (5) Trifluoroacetate versus acetate salt basis on a peptide with seven basic sites — an 8 to 12 percent w/w swing in net peptide content. (6) the rodent ortholog (IGF-1Eb), which carries a different C-terminal sequence from human IGF-1Ec and is sold under the same three letters; a substantial share of the animal literature attributed to this article was performed on that different peptide.

2 Class & testing panel

Form

Single article

Testing panel

P1 — panel definition

3 Primary sources & evidence

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

Published literature exists and is predominantly rodent and in-vitro, from the Goldspink group and successors through the late 1990s and 2000s, using skeletal muscle cell culture and rat models. The human literature is systematically misread in this market and the misreading is specific: most human "MGF" papers measure endogenous IGF-1Ec messenger RNA in muscle biopsies after loading or exercise. They are expression studies, not administration studies, and they do not test the article that is sold. No controlled human trial of administered synthetic 24-residue MGF was identified. A further constraint on the animal data, and it is a chemistry constraint rather than a methodological one: the rodent splice variant IGF-1Eb carries a different C-terminal sequence from human IGF-1Ec, so a substantial share of the animal work was not performed on this peptide at all. The citation index badges each entry with its study type and its species so that neither substitution can be made by a reader in good faith.

4 Storage & specification

Storage

Not offered, so no condition is qualified and no lot is held. The condition that would apply: lyophilized solid, -20 degrees C plus or minus 5 degrees C, desiccated, protected from light. No specific oxidation sensitivity of note — the sequence contains no tryptophan, no methionine and no cysteine — which makes this one of the few peptides in the catalog where light protection and inert headspace would be defaults rather than requirements, and where the governing solid-state issues would instead be hygroscopicity from seven basic sites and Asn deamidation at positions 7 and 9.

Shelf life

Not established. No lot will be purchased, imported or held, so no stability study is opened and no retest interval is assigned.