Thymic peptides and fragments

Thymic peptides were first isolated from thymus extracts, and the name groups molecules that are otherwise unrelated: thymosin α1 and thymosin β4 share no sequence, and thymulin is a nonapeptide studied as its zinc complex. Thymosin β4 is the reference here because TB-500 is a fragment of it.

Members compared

Calculated from each structure

Peptide	Residues	Formula	Monoisotopic mass (Da)	Charge, pH 7	pI	Termini
Thymopentin	5	C30H49N9O9	679.3653	1.0	9.30	free amine; free acid
TB-500	7	C38H68N10O14	888.4916	0.0	7.36	N-acetyl; free acid
Thymulin	9	C33H54N12O15	858.3832	0.0	7.20	pyroglutamate (no free amine); free acid
Thymosin α1	28	C129H215N33O55	3,106.5041	-6.0	3.81	N-acetyl; free acid
Thymosin β4	43	C212H350N56O78S	4,960.4863	-3.0	4.50	N-acetyl; free acid

Sequences and relationships

Each member's sequence in three-letter code, and how it relates to Thymosin β4, worked out position by position from the structures. Members with no entry in the last column are not direct sequence relatives of Thymosin β4.

Relationship to Thymosin β4

Peptide	Sequence	Relationship
Thymopentin	H-Arg-Lys-Asp-Val-Tyr-OH	—
TB-500	Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH	Residues 17–23 of Thymosin β4
Thymulin	H-Pyr-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn-OH	—
Thymosin α1	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	—
Thymosin β4	Ac-Ser-Asp-Lys-Pro-Asp-Met-Ala-Glu-Ile-Glu-Lys-Phe-Asp-Lys-Ser-Lys-Leu-Lys-Lys-Thr-Glu-Thr-Gln-Glu-Lys-Asn-Pro-Leu-Pro-Ser-Lys-Glu-Thr-Ile-Glu-Gln-Glu-Lys-Gln-Ala-Gly-Glu-Ser-OH	Reference sequence

Shared analytical features

The sequence-specific variants from each member's entry, counted across the family: what an HPLC or mass spectrometry result for these peptides is most often read against.

Variants by number of members

Variant	Members
Asparagine deamidation	3 of 5: Thymulin, Thymosin α1, Thymosin β4
Glutamine deamidation	3 of 5: TB-500, Thymulin, Thymosin β4
Methionine oxidation	1 of 5: Thymosin β4

Every member can also carry the synthesis-related variants common to all synthetic peptides, described in How synthetic peptides are made.

Pairs compared in detail

• Thymosin β4 and TB-500 compared

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). Thymic peptides and fragments. Cosmic Peptides Research Library. Retrieved October 26, 2026, from https://cosmicpeptides.com/research/peptides/families/thymic

@misc{cosmicpeptides_research_peptides_families_thymic,
  author       = {{Cosmic Peptides}},
  title        = {Thymic peptides and fragments},
  howpublished = {Cosmic Peptides Research Library},
  year         = {2026},
  month        = oct,
  url          = {https://cosmicpeptides.com/research/peptides/families/thymic},
  urldate      = {2026-10-26},
  note         = {Last reviewed 2026-10-25}
}

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