Fibrinopeptide A

A 16-residue, strongly acidic peptide (human sequence) cleaved from the Aα chain of fibrinogen. 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-Ala-Asp-Ser-Gly-Glu-Gly-Asp-Phe-Leu-Ala-Glu-Gly-Gly-Gly-Val-Arg-OH

One-letter code: ADSGEGDFLA EGGGVR

• 16 residues
• N-terminus: free amine
• C-terminus: free acid

Calculated properties

Calculated from the structure

Property	Value
Molecular formula	C63H97N19O26
CAS Registry Number	25422-31-5
Average molecular weight	1,536.58 g/mol
Monoisotopic mass	1,535.6852 Da
Net charge at pH 7	-3.0
Isoelectric point	3.74
Molar absorption coefficient, 280 nm	No tryptophan, tyrosine or cystine: no absorbance at 280 nm; quantify at 205–220 nm instead.
Hydropathy (GRAVY)	-0.43

Net charge across the pH range

pH 2	pH 4	pH 6	pH 7	pH 8	pH 10	pH 12
1.9	-0.7	-3.0	-3.0	-3.2	-4.0	-4.2

Composition: Gly 5, Ala 2, Asp 2, Glu 2, Arg 1, Leu 1, Phe 1, Ser 1, Val 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]+	1,536.6925
[M+2H]2+	768.8499
[M+3H]3+	512.9023
[M+Na]+	1,558.6744
[M+K]+	1,574.6484

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	1,535.6852	1,536.6925	768.8499	512.9023
M+1	77.2	1,536.6881	1,537.6953	769.3513	513.2366
M+2	34.8	1,537.6907	1,538.6979	769.8526	513.5708
M+3	11.5	1,538.6932	1,539.7005	770.3539	513.9050
M+4	3.1	1,539.6957	1,540.7030	770.8551	514.2392
M+5	0.7	1,540.6981	1,541.7054	771.3563	514.5733

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	72.0444	36.5258	Ala	—	—	16
2	187.0713	94.0393	Asp	1,465.6554	733.3313	15
3	274.1034	137.5553	Ser	1,350.6284	675.8179	14
4	331.1248	166.0661	Gly	1,263.5964	632.3018	13
5	460.1674	230.5873	Glu	1,206.5749	603.7911	12
6	517.1889	259.0981	Gly	1,077.5323	539.2698	11
7	632.2158	316.6116	Asp	1,020.5109	510.7591	10
8	779.2842	390.1458	Phe	905.4839	453.2456	9
9	892.3683	446.6878	Leu	758.4155	379.7114	8
10	963.4054	482.2063	Ala	645.3315	323.1694	7
11	1,092.4480	546.7276	Glu	574.2944	287.6508	6
12	1,149.4695	575.2384	Gly	445.2518	223.1295	5
13	1,206.4909	603.7491	Gly	388.2303	194.6188	4
14	1,263.5124	632.2598	Gly	331.2088	166.1081	3
15	1,362.5808	681.7940	Val	274.1874	137.5973	2
16	—	—	Arg	175.1190	88.0631	1

Immonium ions (low-mass markers of the residues present): Gly 30.0338, Ala 44.0495, Ser 60.0444, Val 72.0808, Leu 86.0964, Asp 88.0393, Glu 102.0550, 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
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). Fibrinopeptide A: peptide reference entry. Cosmic Peptides Research Library. Retrieved October 26, 2026, from https://cosmicpeptides.com/research/peptides/fibrinopeptide-a

@misc{cosmicpeptides_research_peptides_fibrinopeptide_a,
  author       = {{Cosmic Peptides}},
  title        = {Fibrinopeptide A: peptide reference entry},
  howpublished = {Cosmic Peptides Research Library},
  year         = {2026},
  month        = oct,
  url          = {https://cosmicpeptides.com/research/peptides/fibrinopeptide-a},
  urldate      = {2026-10-26},
  note         = {Last reviewed 2026-10-25}
}

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PY  - 2026
DA  - 2026/10/25
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