Substance P (4-11), also called Octa Substance P, is the C-terminal octapeptide Pro-Gln-Gln-Phe-Phe-Gly-Leu-Met-NH₂.

The fragment retains substantial NK1 receptor agonist activity despite removal of the first three residues of full-length Substance P, making it a useful tool for defining the contribution of the C-terminal tachykinin pharmacophore.

Product Information

High NK1 Activity Is Retained After N-Terminal Truncation

Removal of Arg1-Pro2-Lys3 reduces peptide length but leaves the Pro4-Gln-Gln-Phe-Phe-Gly-Leu-Met-NH₂ region intact.

Human NK1 receptor pharmacology data classify SP(4-11) as a full agonist, with reported pIC₅₀ values around 7.7-8.0. This corresponds to activity in the tens-of-nanomolar range under those assay conditions.

We recommend retaining the assay context whenever quantitative potency is reported because receptor expression and functional readout influence apparent potency.

Why SP(4-11) Is Useful for SAR

SP(4-11) sits near a functional boundary in Substance P truncation studies: it is considerably shorter than the native 11-residue peptide yet preserves strong receptor activation.

This makes it useful for comparing which N-terminal residues improve affinity or signaling regulation and which C-terminal residues are sufficient for core NK1 agonist activity.

Research Applications

Substance P (4-11) can support NK1 receptor assays, tachykinin agonist studies, C-terminal pharmacophore research and N-terminal truncation SAR.

Frequently Asked Questions

Is SP(4-11) an NK1 agonist?

Yes. It is classified as a full agonist at the human NK1 receptor in curated pharmacological data.

What is removed relative to full-length Substance P?

Arg1, Pro2 and Lys3 are absent.

Is Met11 retained?

Yes.

Research Use Only.