Thymosin α1

A 28-residue N-acetylated, strongly acidic peptide originally isolated from thymus tissue. 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: Ac-Ser-Asp-Ala-Ala-Val-Asp-Thr-Ser-Ser-Glu-Ile-Thr-Thr-Lys-Asp-Leu-Lys-Glu-Lys-Lys-Glu-Val-Val-Glu-Glu-Ala-Glu-Asn-OH

One-letter code: SDAAVDTSSE ITTKDLKEKK EVVEEAEN

• 28 residues
• N-terminus: N-acetyl
• C-terminus: free acid

Calculated properties

Calculated from the structure

Property	Value
Molecular formula	C129H215N33O55
CAS Registry Number	62304-98-7
Average molecular weight	3,108.32 g/mol
Monoisotopic mass	3,106.5041 Da
Net charge at pH 7	-6.0
Isoelectric point	3.81
Molar absorption coefficient, 280 nm	No tryptophan, tyrosine or cystine: no absorbance at 280 nm; quantify at 205–220 nm instead.
Hydropathy (GRAVY)	-1.03

Net charge across the pH range

pH 2	pH 4	pH 6	pH 7	pH 8	pH 10	pH 12
3.9	-1.0	-5.9	-6.0	-6.0	-6.5	-9.8

Composition: Glu 6, Lys 4, Ala 3, Asp 3, Ser 3, Thr 3, Val 3, Asn 1, Ile 1, Leu 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]+	3,107.5114
[M+2H]2+	1,554.2593
[M+3H]3+	1,036.5087
[M+4H]4+	777.6333
[M+5H]5+	622.3081
[M+Na]+	3,129.4933
[M+K]+	3,145.4673

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). For a molecule this size the monoisotopic peak is not the tallest: the most abundant is M+1. A spectrum read at its tallest peak, or a deconvoluted mass from it, sits about 1.00 Da above the monoisotopic mass.

Isotope peaks (relative abundance, most abundant = 100)

Peak	Abundance	Neutral mass	[M+H]+	[M+2H]2+	[M+3H]3+	[M+4H]4+	[M+5H]5+
M (monoisotopic)	64.0	3,106.5041	3,107.5114	1,554.2593	1,036.5087	777.6333	622.3081
M+1	100.0	3,107.5071	3,108.5143	1,554.7608	1,036.8430	777.8840	622.5087
M+2	84.8	3,108.5098	3,109.5171	1,555.2622	1,037.1772	778.1347	622.7092
M+3	51.2	3,109.5125	3,110.5198	1,555.7635	1,037.5115	778.3854	622.9098
M+4	24.4	3,110.5152	3,111.5225	1,556.2649	1,037.8457	778.6361	623.1103
M+5	9.8	3,111.5178	3,112.5251	1,556.7662	1,038.1799	778.8867	623.3108
M+6	3.4	3,112.5204	3,113.5276	1,557.2675	1,038.5141	779.1374	623.5113
M+7	1.0	3,113.5229	3,114.5302	1,557.7687	1,038.8482	779.3880	623.7119

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	130.0499	65.5286	Ser	—	—	28
2	245.0768	123.0420	Asp	2,978.4688	1,489.7380	27
3	316.1139	158.5606	Ala	2,863.4419	1,432.2246	26
4	387.1510	194.0792	Ala	2,792.4048	1,396.7060	25
5	486.2195	243.6134	Val	2,721.3676	1,361.1875	24
6	601.2464	301.1268	Asp	2,622.2992	1,311.6533	23
7	702.2941	351.6507	Thr	2,507.2723	1,254.1398	22
8	789.3261	395.1667	Ser	2,406.2246	1,203.6159	21
9	876.3581	438.6827	Ser	2,319.1926	1,160.0999	20
10	1,005.4007	503.2040	Glu	2,232.1605	1,116.5839	19
11	1,118.4848	559.7460	Ile	2,103.1180	1,052.0626	18
12	1,219.5325	610.2699	Thr	1,990.0339	995.5206	17
13	1,320.5801	660.7937	Thr	1,888.9862	944.9967	16
14	1,448.6751	724.8412	Lys	1,787.9385	894.4729	15
15	1,563.7021	782.3547	Asp	1,659.8436	830.4254	14
16	1,676.7861	838.8967	Leu	1,544.8166	772.9120	13
17	1,804.8811	902.9442	Lys	1,431.7326	716.3699	12
18	1,933.9237	967.4655	Glu	1,303.6376	652.3224	11
19	2,062.0186	1,031.5130	Lys	1,174.5950	587.8011	10
20	2,190.1136	1,095.5604	Lys	1,046.5000	523.7537	9
21	2,319.1562	1,160.0817	Glu	918.4051	459.7062	8
22	2,418.2246	1,209.6159	Val	789.3625	395.1849	7
23	2,517.2930	1,259.1501	Val	690.2941	345.6507	6
24	2,646.3356	1,323.6714	Glu	591.2257	296.1165	5
25	2,775.3782	1,388.1927	Glu	462.1831	231.5952	4
26	2,846.4153	1,423.7113	Ala	333.1405	167.0739	3
27	2,975.4579	1,488.2326	Glu	262.1034	131.5553	2
28	—	—	Asn	133.0608	67.0340	1

Immonium ions (low-mass markers of the residues present): Ala 44.0495, Ser 60.0444, Val 72.0808, Thr 74.0600, Ile 86.0964, Leu 86.0964, Asn 87.0553, Asp 88.0393, Lys 101.1073, Glu 102.0550.

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
Asparagine deamidation	+0.984 Da	Asparagine at position 28 can deamidate to aspartic or isoaspartic acid through a succinimide intermediate. Moisture, higher pH and warmth speed it up.
Synthesis-related variants	minus a residue (deletion)	As for any synthetic peptide, deletion sequences and incompletely deprotected forms can occur.

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). Thymosin α1: peptide reference entry. Cosmic Peptides Research Library. Retrieved October 26, 2026, from https://cosmicpeptides.com/research/peptides/thymosin-alpha-1

@misc{cosmicpeptides_research_peptides_thymosin_alpha_1,
  author       = {{Cosmic Peptides}},
  title        = {Thymosin α1: peptide reference entry},
  howpublished = {Cosmic Peptides Research Library},
  year         = {2026},
  month        = oct,
  url          = {https://cosmicpeptides.com/research/peptides/thymosin-alpha-1},
  urldate      = {2026-10-26},
  note         = {Last reviewed 2026-10-25}
}

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