PEG-MGF

Both contain the same 24-residue E-domain peptide. MGF is the unmodified peptide, the molecule used in every published study cited here. PEG-MGF adds polyethylene glycol, which raises the mass to roughly 9.8 kDa. The polymer also changes how the conjugate behaves in the lab. It runs at a higher apparent mass on size-exclusion columns and can interfere with antibody-based detection. MGF is the choice for replicating published work. With PEG-MGF, count the PEG chain as an extra variable to control.

PEG-MGF is the PEGylated form of mechano growth factor (MGF), the 24-residue C-terminal E-domain peptide of the IGF-1Ec splice variant of insulin-like growth factor 1. The underlying peptide sequence is Tyr-Gln-Pro-Pro-Ser-Thr-Asn-Lys-Asn-Thr-Lys-Ser-Gln-Arg-Arg-Lys-Gly-Ser-Thr-Phe-Glu-Glu-His-Lys, written YQPPSTNKNTKSQRRKGSTFEEHK, with a molecular weight of approximately 2866 g/mol unmodified and approximately 9.8 kDa in the PEGylated form supplied here. The splice variant was first cloned from mechanically stretched rabbit muscle by Yang, Alnaqeeb, Simpson and Goldspink (J Muscle Res Cell Motil, 1996), and its expression in muscle in response to mechanical load is what the mechano growth factor name records. PEG-MGF is a conjugate rather than a discrete small molecule and carries no CAS registry number on this listing.

The splice biology matters because it defines what the molecule is. The IGF-1Ec transcript carries a 49-base insert in the human sequence, and because the insert is not a multiple of three, the reading frame shifts and the C-terminal E domain is encoded in a different frame from the systemic IGF-1Ea isoform. It is that E-domain peptide, rather than the mature IGF-1 protein, that the early literature connected to muscle repair: the peptide drives myoblast proliferation while blocking differentiation (Yang and Goldspink, FEBS Lett, 2002), appears as an early pulse after local muscle damage in association with satellite cell activation (Hill and Goldspink, J Physiol, 2003), and increased progenitor cell numbers in cultures from normal, dystrophic and ALS muscle (Ates et al., FEBS Lett, 2007). Goldspink's review (Physiology, 2005) frames MGF as the local, damage-triggered isoform, with splicing switching toward IGF-1Ea as repair proceeds.

The PEGylation step is a pharmacokinetic modification, not a change to the peptide chemistry. The unmodified E peptide is cleared from circulation within minutes, so conjugation of polyethylene glycol, raising the mass to roughly 9.8 kDa, is designed to slow clearance through increased hydrodynamic radius, reduced renal filtration and shielding from proteases, the standard logic of the field reviewed by Harris and Chess (Nat Rev Drug Discov, 2003). In primary human muscle cell culture, the unmodified E peptide increased proliferation and delayed senescence in cultures from neonatal and young adult donors but not old adult muscle (Kandalla et al., Mech Ageing Dev, 2011), and in a mouse transplantation model it improved myogenic precursor cell engraftment (Mills et al., Am J Transplant, 2007).

It is worth being direct about the state of the evidence. The primary literature concerns the unmodified E-domain peptide, and the PEGylated form itself has no dedicated peer-reviewed publications, so its behaviour in any assay is an extrapolation from the unmodified molecule and from general PEGylation pharmacology. The founding in-vitro claims have also been challenged directly: a study conducted at two pharmaceutical companies found no effect of the MGF C-terminal peptide, at concentrations up to 500 ng/ml, on the proliferation or differentiation of C2C12 cells, primary human myoblasts or primary mouse muscle stem cells, and concluded that the physiological role of MGF itself should be questioned (Fornaro et al., Am J Physiol Endocrinol Metab, 2014). Human evidence is thin to absent, and the field's own review literature describes MGF as a putative repair factor (Matheny, Nindl and Adamo, Endocrinology, 2010). PEG-MGF is not an approved medicine in any jurisdiction and is supplied as lyophilised powder, supplier-tested at 99.77% purity with batch UKPL-9506, with the certificate published on this page and independent third-party verification pending, for in-vitro laboratory research only.