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

Known as mechano growth factor, MGF is a 24-amino-acid peptide matching the C-terminal E-domain of IGF-1 Ec — an IGF-1 gene splice variant that skeletal muscle expresses more strongly after mechanical loading and injury. It is neither an IGF-1 analogue nor an agonist at IGF-1R. What it is, is the tail end of a precursor protein, and interest in it rests on one arresting observation: separated from the mature IGF-1 it is normally cleaved away from, the E-domain peptide still shows activity of its own.

We supply MGF (Mechano Growth Factor) as lyophilized powder in 2 mg and 5 mg vials, within the IGF and muscle peptides range, for laboratory research only.

Defining MGF

One protein is not what the IGF-1 gene makes. Several pro-IGF-1 transcripts arise by alternative splicing, all containing the same 70-residue mature IGF-1 sequence but differing in the C-terminal extension known as the E-domain. In the IGF-1 Ec variant — the one whose expression climbs steeply in loaded or damaged muscle — that E-domain carries a 49-base insert which shifts the reading frame and yields a distinctive C-terminal sequence. What is made synthetically as MGF is the 24-residue peptide matching that distinctive region.

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

Geoffrey Goldspink's group at the Royal Free Hospital characterised the splice variant during the 1990s while studying how muscle detects and answers mechanical load. Its name reflects the finding rather than the chemistry: in rodent muscle, expression of this transcript rose after stretch and eccentric loading, ahead of the systemic IGF-1 response, which pointed to a locally generated signal.

Two structural details matter when reading this literature. One is that human and rodent E-domain sequences are not identical, so results do not automatically cross between species — a persistent source of confusion in secondary summaries. The other is that MGF as sold is a synthetic fragment of a precursor protein rather than a hormone that circulates naturally; inside the organism the E-domain is cleaved from pro-IGF-1 during processing, and whether the liberated peptide persists in tissue at meaningful concentrations remains unresolved in the field.

The proposed mechanism

MGF has no identified receptor. That is the central caveat about its mechanism, and any account naming one has strayed beyond the published record. What the literature does supply is a collection of cell-level observations: in cultured myoblasts the E-domain peptide has been reported to encourage proliferation and to hold back differentiation into myotubes — the reverse of mature IGF-1, which pushes cells toward differentiation. That opposition is the best argument that the E-domain works by a route of its own rather than by weakly agonising IGF-1R.

Mechanisms put forward in the literature include a membrane interaction driven by the peptide's basic charge, the nuclear or nucleolar localisation described in certain cell studies, and effects on satellite cell activation that would sit well with the mechanical-loading biology behind the name. These are hypotheses resting on cell-culture data, not established mechanism.

With no receptor and a small, heavily charged, unstructured sequence, one practical consequence is extremely brief persistence. Reported stability in solution and in serum is measured in minutes, precisely the problem the PEG-modified variant was created to solve.

What has been studied

Myoblast proliferation and differentiation

C2C12 and primary human myoblasts form the backbone of the cell-based literature, comparing the E-domain peptide with mature IGF-1. Reports describe higher proliferation markers and slower fusion into myotubes, which fits a role in enlarging the satellite cell pool before differentiation gets under way.

Mechanical loading and expression studies

A bigger and sturdier body of work uses no synthetic peptide whatsoever: it quantifies IGF-1 Ec transcript levels in muscle after resistance exercise, stretch or injury, in rodents and in human biopsy studies. Those expression data are what established the loading response, and they say nothing directly about what happens when the synthetic peptide is administered.

Tissue repair and cardiac models

Rodent studies have given the E-domain peptide in muscle injury and cardiac infarct models, reporting shifts in cell survival and regeneration markers. This is exploratory preclinical work with small numbers.

Stability and formulation comparisons

Rapid clearance of the native peptide has generated a separate strand of work comparing it with the PEGylated form. How that choice shapes experimental design is covered in our MGF vs PEG-MGF comparison.

Presentations available

Short in-vitro series suit the 2 mg vial, while the 5 mg vial is more economical where a longer study should stay on one lot. Since the peptide is short-lived once dissolved, most laboratories favour a greater number of small portions over a single large stock. Sourcing checks are in our MGF buying guide, and PEG-MGF is the longer-persisting alternative.

Reconstitution and storage at the bench

The peptide dissolves easily in bacteriostatic or sterile water, its basic residues keeping it comfortably water-soluble, and mildly acidic buffers also feature in the literature. Add solvent down the vial wall onto the cake and swirl instead of shaking, because agitating a 24-residue peptide creates foam and increases surface denaturation without dissolving it any faster.

What follows is laboratory arithmetic rather than a protocol: reconstituting a 5 mg vial with 2 mL of diluent gives 2.5 mg/mL, that is 2,500 mcg/mL, so 0.1 mL — the 10-unit mark on a U-100 syringe — holds 250 mcg. Using 5 mL on the same vial gives 1 mg/mL and 100 mcg per 0.1 mL. The method is in our reconstitution guide.

Keep lyophilized vials sealed at −20 °C, protected from light and moisture. Once reconstituted, MGF has only a brief working window at 2–8 °C; anything longer than a few days calls for aliquoting and freezing, and repeated freeze-thaw cycles should be avoided. Broader practice is covered in how to store peptides.

Purity, the COA and how to read it

Two entries do most of the work on an MGF certificate. Purity comes from the HPLC trace as main-peak area, and with a basic 24-mer the shoulders are what count: sequences short by one residue elute close to the main peak, so a symmetrical, clean peak tells you more than the percentage by itself. Mass spectrometry should give an observed value agreeing with 2,867.10 g/mol; a reading 17 Da below that would indicate a deamidation or truncation issue worth raising.

The counter-ion belongs on the document too. Reversed-phase purification generally leaves peptides as a trifluoroacetate salt, and with a peptide this basic the salt fraction is far from negligible — it changes how much peptide a nominally 5 mg vial really holds. Each section is dealt with in turn in our guide to reading a peptide certificate of analysis.

Regulatory position

Neither in the United States nor elsewhere does MGF hold a marketing authorisation as a medicine; there is no reference-listed product and no approved labelling. No approved use exists for it in any form. Anti-doping rules prohibit IGF-1 and its splice-variant peptides in sport.

Related peptides and further reading

PEG-MGF is the direct alternative: the same core peptide with a polyethylene glycol chain attached to lengthen its working life. Receptor-active members of the family are IGF-1 LR3 and IGF-1 DES (1-3), which act at IGF-1R and so address a different question from the E-domain peptide. For wider context on the tissue biology, see our skeletal muscle research hub.