MGF: The IGF-1 Ec E-Domain Peptide, Its Open Mechanism and Short Working Life

MGF — mechano growth factor — is a 24-residue peptide corresponding to the C-terminal E-domain of IGF-1 Ec, a splice form of the IGF-1 gene whose expression in skeletal muscle rises after mechanical loading or damage. It is not a modified IGF-1, and it does not activate IGF-1R. It is the tail of a precursor protein, and the reason anyone studies it is a striking finding: once detached from the mature IGF-1 that it is normally trimmed from, the E-domain appears to have biological activity in its own right.

MGF (Mechano Growth Factor) is available from us freeze-dried in 2 mg and 5 mg vials, listed with the IGF and muscle peptides and sold for laboratory research only.

Defining MGF

The IGF-1 gene does not produce just one protein. Alternative splicing generates several pro-IGF-1 transcripts; all share the 70-residue mature IGF-1 sequence but end in different C-terminal extensions, the E-domains. In the Ec variant — the transcript that climbs sharply in stressed or injured muscle — a 49-base insertion in the E-domain shifts the reading frame and produces a unique C-terminal sequence. Synthetic MGF is the 24-amino-acid peptide corresponding to that unique stretch.

The sequence supplied reads Tyr-Gln-Pro-Pro-Ser-Thr-Asn-Lys-Asn-Thr-Lys-Ser-Gln-Arg-Arg-Lys-Gly-Ser-Thr-Phe-Glu-Glu-Arg-Lys; its CAS number is 62031-54-3 and its molecular weight 2,867.10 g/mol. Abundant arginine and lysine make the peptide strongly basic, which bears on its behaviour both in solution and on a chromatography column.

Origin and structure

The variant was described in the 1990s by Geoffrey Goldspink and colleagues at the Royal Free Hospital in London, who were investigating how muscle senses mechanical strain and responds to it. The name records what they saw, not what the molecule is: after stretching or eccentric exercise in rodent muscle, this transcript increased before any rise in circulating IGF-1, suggesting a signal produced locally in the tissue.

Keep two structural points in mind when reading the papers. First, the E-domain sequence differs between humans and rodents, so findings cannot simply be transferred from one species to the other — something secondary sources regularly overlook. Second, commercial MGF is a synthetic piece of a precursor, not a naturally circulating hormone. Inside the organism, the E-domain is removed from pro-IGF-1 during maturation, and it is still an open question whether the released peptide survives in tissue at concentrations that matter.

The proposed mechanism

No receptor for MGF has been found. That is the single most important caveat about how it works, and any description that names a receptor has gone beyond the evidence. What published work does provide is a set of observations in cells. In myoblast cultures, the E-domain peptide has been reported to stimulate proliferation and delay fusion into myotubes — the opposite of mature IGF-1, which drives differentiation. That contrast is the strongest indication that the E-domain acts through a distinct mechanism, not as a feeble IGF-1R agonist.

Suggested mechanisms include interaction with the cell membrane via the peptide's positive charge, localisation to the nucleus or nucleolus seen in some cell experiments, and effects on satellite-cell activation that would fit the mechanical-loading story behind its name. All of these are hypotheses drawn from cell culture, not established pathways.

One practical consequence of being small, highly charged, unstructured and receptorless is that the peptide barely lasts. Published figures for its stability in solution and in serum are on the order of minutes — exactly the limitation the PEG-modified version was made to overcome.

What has been studied

Myoblast proliferation and differentiation

Most of the cell-based literature rests on C2C12 cells and primary human myoblasts, set side by side with mature IGF-1. What is reported is increased proliferation markers alongside delayed fusion into myotubes — consistent with expanding the satellite cell population before differentiation begins.

Mechanical loading and expression studies

A larger and more robust literature involves no synthetic peptide at all. It measures how much IGF-1 Ec mRNA muscle contains after resistance exercise, stretch or injury, both in rodents and in human biopsies. Those expression studies are what demonstrated the response to loading — and they tell us nothing directly about what giving the synthetic peptide would do.

Tissue repair and cardiac models

In rodents, the E-domain peptide has been tested in models of muscle injury and myocardial infarction, with reported changes in markers of cell survival and regeneration. These are small, exploratory preclinical studies.

Stability and formulation comparisons

Because the unmodified peptide clears so quickly, a separate strand of work compares it directly with the PEGylated form. Our MGF vs PEG-MGF comparison explains how that choice affects experimental design.

Presentations available

For brief in-vitro series the 2 mg vial is enough; for a longer study that should use one lot throughout, the 5 mg vial is better value. Because the peptide does not last long in solution, most labs prefer many small portions to one big stock. What to check when sourcing is in our MGF buying guide, and PEG-MGF is the option that persists longer.

Reconstitution and storage at the bench

Thanks to its basic residues, MGF dissolves readily in bacteriostatic or sterile water; some published methods use slightly acidic buffers instead. Run the solvent down the glass onto the cake and swirl rather than shake — agitating a peptide of 24 residues produces foam and more denaturation at the surface, and it does not speed up dissolution.

The numbers below are bench arithmetic, not a protocol. A 5 mg vial made up with 2 mL of diluent is at 2.5 mg/mL (2,500 mcg/mL), so each 0.1 mL — ten units on a U-100 syringe, i.e. the 10-unit line — carries 250 mcg. Made up with 5 mL instead, the same vial gives 1 mg/mL, or 100 mcg in each 0.1 mL. See the reconstitution guide for the method.

Unopened freeze-dried vials should stay sealed at −20 °C, dry and dark. After reconstitution, MGF is usable for only a short time at 2–8 °C; for anything beyond a few days, aliquot and freeze, and do not thaw and refreeze repeatedly. General practice is described in how to store peptides.

Purity, the COA and how to read it

On an MGF certificate, two items carry most of the information. HPLC purity is given as main-peak area, and for a basic 24-mer the shoulders deserve the closest look: single-residue deletion sequences run right next to the main peak, so a clean, symmetrical peak says more than the number alone. The mass-spec result should show an observed value agreeing with 2,867.10 g/mol; a value 17 Da lower points to deamidation or truncation and is worth querying.

The certificate should also state the counter-ion. After reversed-phase purification peptides usually carry trifluoroacetate salt, and with a sequence this basic the salt makes up a significant share of the weight — it alters the real peptide content of a vial labelled 5 mg. Our guide to reading a peptide certificate of analysis goes through each section.

Regulatory position

MGF is not authorised as a medicine in the United States, the EU or anywhere else; no reference product or approved label exists, and it has no approved use in any form. Sport anti-doping rules ban IGF-1 and its splice-variant peptides.

Related peptides and further reading

The closest alternative is PEG-MGF — the same core sequence with a polyethylene glycol chain added so it lasts longer. The family members that do activate the receptor, IGF-1 LR3 and IGF-1 DES (1-3), work through IGF-1R and therefore address a different research question from the E-domain peptide. Our skeletal muscle research hub gives broader tissue context.

Matching catalogue section: IGF & Muscle Peptides