Substance P

An undecapeptide amide of the tachykinin family, ending in the Phe-X-Gly-Leu-Met-NH2 motif the family shares. Every value on this page is calculated from the structure shown, by the method and constants in the sources below; measured values for a particular lot are on its certificate of analysis.

Structure

Three-letter code: H-Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-Met-NH2

One-letter code: RPKPQQFFGL M

• 11 residues
• N-terminus: free amine
• C-terminus: amide

Calculated properties

Calculated from the structure

Property	Value
Molecular formula	C63H98N18O13S
CAS Registry Number	33507-63-0
Average molecular weight	1,347.65 g/mol
Monoisotopic mass	1,346.7281 Da
Net charge at pH 7	3.0
Isoelectric point	No acidic groups: the peptide carries a positive charge at every pH, so it has no isoelectric point.
Molar absorption coefficient, 280 nm	No tryptophan, tyrosine or cystine: no absorbance at 280 nm; quantify at 205–220 nm instead.
Hydropathy (GRAVY)	-0.70

Net charge across the pH range

pH 2	pH 4	pH 6	pH 7	pH 8	pH 10	pH 12
3.0	3.0	3.0	3.0	2.8	1.9	0.8

Composition: Gln 2, Phe 2, Pro 2, Arg 1, Gly 1, Leu 1, Lys 1, Met 1.

Expected mass spectrometry ions

The protonated ions expected in positive-mode electrospray, from the monoisotopic mass, and the common sodium and potassium adducts. MALDI spectra show mainly [M+H]⁺.

Expected ions (monoisotopic)

Ion	m/z
[M+H]+	1,347.7354
[M+2H]2+	674.3713
[M+3H]3+	449.9167
[M+Na]+	1,369.7174
[M+K]+	1,385.6913

Isotope pattern

Natural carbon-13, nitrogen-15, oxygen-18, sulfur-34 and deuterium spread each ion over a cluster of peaks about 1 Da apart (1/z on the m/z scale). The monoisotopic peak is the most abundant.

Isotope peaks (relative abundance, most abundant = 100)

Peak	Abundance	Neutral mass	[M+H]+	[M+2H]2+	[M+3H]3+
M (monoisotopic)	100.0	1,346.7281	1,347.7354	674.3713	449.9167
M+1	77.1	1,347.7310	1,348.7382	674.8728	450.2509
M+2	36.5	1,348.7325	1,349.7398	675.3735	450.5848
M+3	12.8	1,349.7338	1,350.7410	675.8742	450.9185
M+4	3.6	1,350.7352	1,351.7424	676.3749	451.2523
M+5	0.8	1,351.7367	1,352.7440	676.8756	451.5862

Fragment ions (MS/MS)

Collision-induced fragmentation breaks peptide bonds along the backbone. Fragments that keep the N-terminus are b ions; those that keep the C-terminus are y ions. Reading the ladder confirms the sequence residue by residue. Singly charged monoisotopic values, with doubly charged values beside them. The b ion containing every residue is rarely seen and the y ion containing every residue is the precursor itself, so neither is listed.

b and y ions

b#	b+	b2+	Residue	y+	y2+	y#
1	157.1084	79.0578	Arg	—	—	11
2	254.1612	127.5842	Pro	1,191.6343	596.3208	10
3	382.2561	191.6317	Lys	1,094.5815	547.7944	9
4	479.3089	240.1581	Pro	966.4866	483.7469	8
5	607.3675	304.1874	Gln	869.4338	435.2205	7
6	735.4260	368.2167	Gln	741.3752	371.1913	6
7	882.4944	441.7509	Phe	613.3167	307.1620	5
8	1,029.5629	515.2851	Phe	466.2483	233.6278	4
9	1,086.5843	543.7958	Gly	319.1798	160.0936	3
10	1,199.6684	600.3378	Leu	262.1584	131.5828	2
11	—	—	Met	149.0743	75.0408	1

Immonium ions (low-mass markers of the residues present): Gly 30.0338, Pro 70.0651, Leu 86.0964, Gln 101.0709, Lys 101.1073, Met 104.0528, Phe 120.0808, Arg 129.1135.

What to watch for analytically

Variants this sequence can give, from its chemistry. They are what an HPLC or mass spectrometry result for this peptide is read against; none is a statement about a particular lot. Where synthesis variants come from is explained in How synthetic peptides are made.

Sequence-specific variants

Variant	Mass change	Why
Methionine oxidation	+15.995 Da per oxidized residue	Methionine at position 11 can oxidize to the sulfoxide, which usually elutes slightly earlier in reversed-phase HPLC.
Glutamine deamidation	+0.984 Da	Glutamine at positions 5 and 6 can also deamidate, much more slowly than asparagine.
C-terminal amide	free-acid variant +0.984 Da	The C-terminus is an amide. The corresponding free acid, from synthesis or hydrolysis, differs by +0.984 Da, close to the isotope spacing, so it needs a resolved spectrum to tell apart.
Synthesis-related variants	e.g. +252.082 Da (Pbf), minus a residue (deletion)	As for any synthetic peptide, deletion sequences and incompletely deprotected forms can occur; on arginine, a residual Pbf protecting group adds 252.082 Da.

Sources & Further Reading

1. Prohaska T, Irrgeher J, Benefield J, Böhlke JK, Chesson LA, Coplen TB, et al. Standard atomic weights of the elements 2021 (IUPAC Technical Report). Pure and Applied Chemistry 2022;94(5):573–600. doi:10.1515/pac-2019-0603
2. Wang M, Huang WJ, Kondev FG, Audi G, Naimi S. The AME 2020 atomic mass evaluation (II). Tables, graphs and references. Chinese Physics C 2021;45(3):030003. doi:10.1088/1674-1137/abddaf
3. Rice P, Longden I, Bleasby A. EMBOSS: the European Molecular Biology Open Software Suite. Trends in Genetics 2000;16(6):276–277. doi:10.1016/S0168-9525(00)02024-2
4. Pace CN, Vajdos F, Fee L, Grimsley G, Gray T. How to measure and predict the molar absorption coefficient of a protein. Protein Science 1995;4(11):2411–2423. doi:10.1002/pro.5560041120
5. Kyte J, Doolittle RF. A simple method for displaying the hydropathic character of a protein. Journal of Molecular Biology 1982;157(1):105–132. doi:10.1016/0022-2836(82)90515-0
6. Meija J, Coplen TB, Berglund M, Brand WA, De Bièvre P, Gröning M, et al. Isotopic compositions of the elements 2013 (IUPAC Technical Report). Pure and Applied Chemistry 2016;88(3):293–306. doi:10.1515/pac-2015-0503
7. Roepstorff P, Fohlman J. Letter to the editors: proposal for a common nomenclature for sequence ions in mass spectra of peptides. Biomedical Mass Spectrometry 1984;11(11):601. doi:10.1002/bms.1200111109
8. Biemann K. Contributions of mass spectrometry to peptide and protein structure. Biomedical and Environmental Mass Spectrometry 1988;16(1–12):99–111. doi:10.1002/bms.1200160119
9. Geiger T, Clarke S. Deamidation, isomerization, and racemization at asparaginyl and aspartyl residues in peptides. Succinimide-linked reactions that contribute to protein degradation. Journal of Biological Chemistry 1987;262(2):785–794. doi:10.1016/S0021-9258(19)75855-4
10. Manning MC, Chou DK, Murphy BM, Payne RW, Katayama DS. Stability of protein pharmaceuticals: an update. Pharmaceutical Research 2010;27(4):544–575. doi:10.1007/s11095-009-0045-6
11. D'Hondt M, Bracke N, Taevernier L, Gevaert B, Verbeke F, Wynendaele E, et al. Related impurities in peptide medicines. Journal of Pharmaceutical and Biomedical Analysis 2014;101:2–30. doi:10.1016/j.jpba.2014.06.012

Cosmic Peptides. (2026, October 25). Substance P: peptide reference entry. Cosmic Peptides Research Library. Retrieved October 26, 2026, from https://cosmicpeptides.com/research/peptides/substance-p

@misc{cosmicpeptides_research_peptides_substance_p,
  author       = {{Cosmic Peptides}},
  title        = {Substance P: peptide reference entry},
  howpublished = {Cosmic Peptides Research Library},
  year         = {2026},
  month        = oct,
  url          = {https://cosmicpeptides.com/research/peptides/substance-p},
  urldate      = {2026-10-26},
  note         = {Last reviewed 2026-10-25}
}

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DA  - 2026/10/25
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