ACTH fragment names can look almost interchangeable when a title contains only a pair of residue numbers. They are not. Different boundaries retain different parts of the parent hormone, and analogue names can describe substitutions rather than a simple cut from the native sequence. This guide shows how to make the molecular comparison before interpreting the biology.
Start with the parent and count inclusively
The official Cortrosyn description identifies cosyntropin as the first 24 residues of the 39-residue ACTH molecule. Its numbered sequence provides a direct reference for these amino-terminal positions.DailyMed — Cortrosyn cosyntropin description (opens in a new tab)
A fragment interval includes both endpoints. ACTH(4–10) therefore contains seven residues, while ACTH(1–24) contains 24. The second number is a position in the parent, not the fragment’s length.
| Written interval | Inclusive length | Positions excluded |
|---|---|---|
| ACTH(1–24) | 24 residues | Parent positions 25–39 |
| ACTH(4–10) | 7 residues | Positions before 4 and after 10 |
| ACTH(4–7) | 4 residues | Positions before 4 and after 7 |
For any publication, establish whether the numbering refers to mature ACTH or a longer precursor. A matching pair of numbers is meaningful only when the reference sequence is also the same.
Then record terminal groups and stereochemistry. An interval identifies sequence coverage but does not fully specify every possible synthetic chemical form of that segment.
A seven-residue analogue need not be the native seven residues
The numbered cosyntropin sequence gives native ACTH positions 4–10 as Met-Glu-His-Phe-Arg-Trp-Gly. PubChem records Semax as Met-Glu-His-Phe-Pro-Gly-Pro and associates it with ACTH(4–7)-Pro-Gly-Pro terminology.DailyMed — Cortrosyn cosyntropin description (opens in a new tab)PubChem — ACTH(4–7)-Pro-Gly-Pro / Semax (opens in a new tab)
Both sequences contain seven residues, but their final three differ. Semax retains the four-residue ACTH segment and includes Pro-Gly-Pro; it is not simply the unchanged native ACTH(4–10) segment.
| Material | Sequence |
|---|---|
| Native ACTH positions 4–10 | MEHFRWG |
| Semax | MEHFPGP |
This is why an older paper describing an ACTH-fragment analogue needs a methods-level identity check. The word analogue can carry a modification that a shortened search-result title hides.
A fragment label does not predict the outcome direction
Born and colleagues’ 1987 ACTH(4–10) study examined auditory event-related potentials in twelve men under a double-blind comparison design. It reported a reduction in an electrophysiological measure related to selective attention, rather than a uniform enhancement of attention measures.Born and colleagues — ACTH(4–10) and electrophysiological attention measures (opens in a new tab)
The available abstract is truncated, so this reference does not infer unreported numerical results or a complete clinical interpretation from it. The useful point is that the paper identifies both a particular fragment and a particular measured response.
That experiment should not be relabelled as a Semax trial. It also should not be used to predict every effect of the full ACTH hormone or another fragment.
Likewise, an adrenal-response experiment and an electrophysiological attention experiment need separate outcome fields. Sharing a parent hormone does not make the endpoints equivalent or establish a common benefit.
Make a sequence-to-evidence map before writing a conclusion
For each study, write the reference sequence, retained positions, substitutions and terminal chemistry. Add the species, preparation and endpoint only after the molecular entry is clear.
If a review uses several names for one preparation, reconcile them against its sequence. If it uses one broad name for several preparations, split the entries. Both errors can distort how much direct evidence exists.
This mapping does not require assuming that every structural difference produces a different effect. It requires recognising that equivalence is a question to test, not a consequence of a shared abbreviation.
Sources and further detail
- DailyMed — Cortrosyn cosyntropin description (opens in a new tab)
Official description and numbered ACTH(1–24) sequence checked. Used for identity and residue mapping only; no diagnostic or administration guidance.
- PubChem — ACTH(4–7)-Pro-Gly-Pro / Semax (opens in a new tab)
Official sequence and alias fields read. Comparison identifies the differing final three residues; no clinical inference drawn from database categories.
- Born and colleagues — ACTH(4–10) and electrophysiological attention measures (opens in a new tab)
Original 1987 indexed abstract read. Its twelve-person design and specific electrophysiological result retained; the abstract is explicitly truncated and no missing outcome is inferred.
Sources checked 19 September 2026. Worked examples are illustrative unless a supplied report is explicitly identified. This article has not undergone independent scientific peer review.