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Substance P Free Acid contains the complete 11-residue Substance P sequence but terminates in Met-OH instead of the native Met-NH2 amide. This single terminal change produces a chemically distinct peptide without altering the residue sequence.
The free-acid analog shows markedly reduced Substance P-like biological activity and provides a strong control for studying the importance of C-terminal amidation. It is especially useful in NK1 receptor SAR, peptide-processing and terminal-chemistry experiments.
Product Information
| Product Name | Substance P, Free Acid |
| Catalog No. | AS2723 |
| CAS No. | 71977-09-8 |
| Sequence | Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-Met-OH |
| One-Letter Sequence | RPKPQQFFGLM-OH |
| Peptide Length | 11 residues |
| Molecular Formula | C63H97N17O14S |
| Molecular Weight | Approximately 1348.6 Da |
| C-Terminus | Met-OH |
C-Terminal Amidation Is Part of the Tachykinin Pharmacophore
Native Substance P terminates in Met-NH2. Conversion to Met-OH changes terminal charge and hydrogen-bonding behavior and strongly affects biological activity.
This illustrates why two peptides with the same amino acid sequence should not be considered equivalent when terminal chemistry differs.
A Useful Terminal-Chemistry Control
We recommend pairing Substance P Free Acid with native Substance P when testing the specific contribution of C-terminal amidation.
Research Applications
The peptide can support NK1 structure–activity studies, peptide amidation research, terminal-group comparisons and negative- or low-activity control design.
Frequently Asked Questions
What is different from native Substance P?
Only the terminal functional group: Met-OH replaces Met-NH2.
Does the free acid retain full Substance P activity?
No. Loss of the C-terminal amide markedly reduces Substance P-like activity.
Is it the same molecular weight as native Substance P?
No.