What is Semax made from?

It is the ACTH (4-7) fragment — Met-Glu-His-Phe — with a Pro-Gly-Pro tail appended. The tail is not part of the ACTH sequence; it was added to slow enzymatic degradation.

Why does Semax contain Pro-Gly-Pro?

Proline constrains the backbone and proline-rich terminals resist exopeptidase attack, so the tail slows enzymatic degradation of what is otherwise a very short peptide. Selank uses the same tail on a different parent fragment.

Why is Semax sensitive to oxidation?

It carries a methionine at position one, and an N-terminal methionine is particularly exposed. Oxidation adds 16 daltons and shows as a shoulder on the main HPLC peak, which is missed by reading the purity figure alone.

Identification·2 min read

Semax — an ACTH fragment with a Pro-Gly-Pro tail

Semax is ACTH (4-7) with a proline-glycine-proline tail attached. That tail is a design decision shared with Selank, and it explains both compounds.

Semax is a seven-residue peptide, CAS 80714-61-0, molecular formula C37H51N9O10S, molecular weight 813.91 g/mol. Its sequence is Met-Glu-His-Phe-Pro-Gly-Pro — the ACTH (4-7) fragment carrying an appended proline-glycine-proline tail. That tail is a stabilising design shared with Selank, and understanding it once explains both compounds.

By the Bench Grade Research Team · Last updated October 7, 2026

Semax identity data

Identity
Property	Value
CAS Registry Number	80714-61-0
Molecular formula	C37H51N9O10S
Molecular weight	813.91 g/mol
Sequence	Met-Glu-His-Phe-Pro-Gly-Pro
Derived from	ACTH (4-7) plus Pro-Gly-Pro

What the Pro-Gly-Pro tail is for

The first four residues, Met-Glu-His-Phe, correspond to residues 4 to 7 of adrenocorticotropic hormone. The final three, Pro-Gly-Pro, are not part of that fragment — they were appended deliberately.

Proline constrains the peptide backbone and proline-rich terminals resist exopeptidase attack, so a Pro-Gly-Pro tail is a recognised way to slow enzymatic degradation of a short peptide. Selank uses the same tail on a different parent fragment, which is the clearest example in this market of one structural idea applied twice.

The methionine governs storage

The sulfur in the formula is a methionine at position one, and an N-terminal methionine is particularly exposed. Oxidation adds 16 daltons and appears as a shoulder on the main HPLC peak rather than a distinct impurity, so peak shape matters more than the purity number here.

What the published work examined

Two studies in our research library, from 2007 and 2018, are clinical and animal investigations concerning neurological parameters. They are linked below and describe research findings only.

References

Primary literature for the compounds discussed above. Links open the record on PubMed.

The efficacy of semax in the treatment of patients at different stages of ischemic stroke Gusev EI, et al. Zh Nevrol Psikhiatr Im S S Korsakova. 2018. PMID 29798983 → · summary
The mitochondrial-derived peptide MOTS-c is a regulator of plasma metabolites and enhances insulin sensitivity Kim SJ, et al. Physiol Rep. 2019. PMID 31293078 → · summary
The Mitochondrial-Derived Peptide MOTS-c Promotes Metabolic Homeostasis and Reduces Obesity and Insulin Resistance Lee C, et al. Cell Metab. 2015. PMID 25738459 → · summary
The Mitochondrial-Derived Peptide MOTS-c Promotes Metabolic Homeostasis and Reduces Obesity and Insulin Resistance Lee C, et al. Cell Metab. 2015. PMID 25738459 → · summary
Neuroprotective and antiamnesic effects of Semax during experimental ischemic infarction of the cerebral cortex Stavchansky VV, et al. Bull Exp Biol Med. 2007. PMID 17603664 → · summary

Primary sources

Frequently asked questions

What is Semax made from?: It is the ACTH (4-7) fragment — Met-Glu-His-Phe — with a Pro-Gly-Pro tail appended. The tail is not part of the ACTH sequence; it was added to slow enzymatic degradation.
Why does Semax contain Pro-Gly-Pro?: Proline constrains the backbone and proline-rich terminals resist exopeptidase attack, so the tail slows enzymatic degradation of what is otherwise a very short peptide. Selank uses the same tail on a different parent fragment.
Why is Semax sensitive to oxidation?: It carries a methionine at position one, and an N-terminal methionine is particularly exposed. Oxidation adds 16 daltons and shows as a shoulder on the main HPLC peak, which is missed by reading the purity figure alone.

Compounds discussed in this guide

Who publishes this guide

Who sells it: Bench Grade Peptides LLC, a US supplier of lyophilized synthetic peptides for laboratory research use only. It works with US manufacturing partners rather than running a facility of its own. Is Bench Grade Peptides legit? →
Certificates of Analysis: 139 third-party Certificates of Analysis covering 39 of 44 live products, published per lot in a public library anyone can read before ordering. A very recent lot can appear a few days after it enters the catalogue. COA library →
Ships from: Florida, by UPS, to US addresses only (no international shipping). The registered address in Dover, Delaware is the legal address only. Shipping →
Use: For laboratory research use only — not for human or veterinary use. Not a drug, supplement or medical device. Compliance and research use →

All products discussed in this guide are supplied by Bench Grade Peptides for laboratory research use only. Not for human or veterinary use.