Thymulin and Thymosin α1 compared

Two thymic peptides with no shared sequence. Thymulin is a nine-residue peptide with an N-terminal pyroglutamate that binds zinc; thymosin α1 is a 28-residue N-acetylated peptide, rich in acidic residues, with a free C-terminal acid. Their masses differ by more than a factor of three.

Sequences side by side

Aligned from residue 1: 1 position identical, 8 substituted, 19 present in only one. In each column the upper residue is Thymulin's and the lower is Thymosin α1's. Substituted positions are highlighted.

Termini and bridges also differ: N-terminus: Thymulin pyroglutamate (no free amine), Thymosin α1 N-acetyl.

Calculated properties

Calculated from each structure

Property	Thymulin	Thymosin α1	Difference (Thymosin α1 − Thymulin)
Residues	9	28	+19
Molecular formula	C33H54N12O15	C129H215N33O55
Monoisotopic mass (Da)	858.3832	3,106.5041	+2,248.1210
Average mass (g/mol)	858.86	3,108.32	+2,249.45
Net charge at pH 7	0.0	-6.0	−6.0
Isoelectric point	7.20	3.81	−3.39
Hydropathy (GRAVY)	not calculated	-1.03
ε280 (M−1 cm−1)	0	0

Telling them apart by mass spectrometry

The monoisotopic masses differ by 2,248.1210 Da, which any routine mass spectrometer resolves.

Expected protonated ions (monoisotopic m/z)

Ion	Thymulin	Thymosin α1
[M+H]+	859.3904	3,107.5114
[M+2H]2+	430.1989	1,554.2593
[M+3H]3+	287.1350	1,036.5087
[M+4H]4+	215.6031	777.6333

Telling them apart by HPLC

They differ greatly in size (9 and 28 residues), so their reversed-phase retention cannot be estimated from average hydropathy; size, charge and the residues at the ends all contribute. They are usually well separated. Retention depends on the whole molecule and on the method, so the order is confirmed by running both, or by mass spectrometry of each peak.

Analytical variants each can form

The sequence-specific variants from each entry. A variant only one of them can form is a quick way to tell which is which, and a reminder of what to look for in each.

Sequence-specific variants

Variant	Mass change	Thymulin	Thymosin α1
Asparagine deamidation	+0.984 Da	Yes	Yes
Glutamine deamidation	+0.984 Da	Yes	No

Full details, with isotope patterns and fragment ions, are on each entry: Thymulin and Thymosin α1. Both are compared with the rest of their family on the family page.

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 29). Thymulin and Thymosin α1 compared. Cosmic Peptides Research Library. Retrieved November 2, 2026, from https://cosmicpeptides.com/research/peptides/compare/thymulin-vs-thymosin-alpha-1

@misc{cosmicpeptides_research_peptides_compare_thymulin_vs_thymosin_alpha_1,
  author       = {{Cosmic Peptides}},
  title        = {Thymulin and Thymosin α1 compared},
  howpublished = {Cosmic Peptides Research Library},
  year         = {2026},
  month        = oct,
  url          = {https://cosmicpeptides.com/research/peptides/compare/thymulin-vs-thymosin-alpha-1},
  urldate      = {2026-11-02},
  note         = {Last reviewed 2026-10-29}
}

TY  - ELEC
AU  - Cosmic Peptides
TI  - Thymulin and Thymosin α1 compared
T2  - Cosmic Peptides Research Library
PB  - Cosmic Peptides
PY  - 2026
DA  - 2026/10/29
UR  - https://cosmicpeptides.com/research/peptides/compare/thymulin-vs-thymosin-alpha-1
Y2  - 2026/11/02
LA  - en
ER  -