Thymosin β4

A 43-residue, N-acetylated, strongly acidic and lysine-rich peptide. The TB-500 fragment, Ac-LKKTETQ, is its residues 17–23. 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-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

One-letter code: SDKPDMAEIE KFDKSKLKKT ETQEKNPLPS KETIEQEKQA GES

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

Calculated properties

Calculated from the structure

Property	Value
Molecular formula	C212H350N56O78S
CAS Registry Number	77591-33-4
Average molecular weight	4,963.51 g/mol
Monoisotopic mass	4,960.4863 Da
Net charge at pH 7	-3.0
Isoelectric point	4.50
Molar absorption coefficient, 280 nm	No tryptophan, tyrosine or cystine: no absorbance at 280 nm; quantify at 205–220 nm instead.
Hydropathy (GRAVY)	-1.70

Net charge across the pH range

pH 2	pH 4	pH 6	pH 7	pH 8	pH 10	pH 12
8.9	3.1	-2.9	-3.0	-3.0	-4.2	-11.5

Composition: Lys 9, Glu 8, Ser 4, Asp 3, Gln 3, Pro 3, Thr 3, Ala 2, Ile 2, Leu 2, Asn 1, Gly 1, Met 1, Phe 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]+	4,961.4936
[M+2H]2+	2,481.2504
[M+3H]3+	1,654.5027
[M+4H]4+	1,241.1289
[M+5H]5+	993.1045
[M+6H]6+	827.7550
[M+Na]+	4,983.4755
[M+K]+	4,999.4495

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+2. A spectrum read at its tallest peak, or a deconvoluted mass from it, sits about 2.01 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+6H]6+
M (monoisotopic)	28.5	4,960.4863	4,961.4936	2,481.2504	1,654.5027	1,241.1289	993.1045	827.7550
M+1	73.4	4,961.4892	4,962.4965	2,481.7519	1,654.8370	1,241.3796	993.3051	827.9221
M+2	100.0	4,962.4919	4,963.4992	2,482.2532	1,655.1712	1,241.6303	993.5057	828.0893
M+3	95.2	4,963.4945	4,964.5017	2,482.7545	1,655.5054	1,241.8809	993.7062	828.2564
M+4	70.9	4,964.4969	4,965.5042	2,483.2557	1,655.8396	1,242.1315	993.9067	828.4234
M+5	43.8	4,965.4993	4,966.5066	2,483.7569	1,656.1737	1,242.3821	994.1071	828.5905
M+6	23.2	4,966.5017	4,967.5089	2,484.2581	1,656.5078	1,242.6327	994.3076	828.7576
M+7	10.9	4,967.5040	4,968.5112	2,484.7593	1,656.8419	1,242.8833	994.5081	828.9246
M+8	4.6	4,968.5062	4,969.5135	2,485.2604	1,657.1760	1,243.1338	994.7085	829.0916
M+9	1.8	4,969.5085	4,970.5158	2,485.7615	1,657.5101	1,243.3844	994.9090	829.2587
M+10	0.6	4,970.5108	4,971.5180	2,486.2627	1,657.8442	1,243.6350	995.1094	829.4257

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	—	—	43
2	245.0768	123.0420	Asp	4,832.4510	2,416.7291	42
3	373.1718	187.0895	Lys	4,717.4241	2,359.2157	41
4	470.2245	235.6159	Pro	4,589.3291	2,295.1682	40
5	585.2515	293.1294	Asp	4,492.2763	2,246.6418	39
6	716.2920	358.6496	Met	4,377.2494	2,189.1283	38
7	787.3291	394.1682	Ala	4,246.2089	2,123.6081	37
8	916.3717	458.6895	Glu	4,175.1718	2,088.0895	36
9	1,029.4557	515.2315	Ile	4,046.1292	2,023.5682	35
10	1,158.4983	579.7528	Glu	3,933.0451	1,967.0262	34
11	1,286.5933	643.8003	Lys	3,804.0025	1,902.5049	33
12	1,433.6617	717.3345	Phe	3,675.9076	1,838.4574	32
13	1,548.6887	774.8480	Asp	3,528.8392	1,764.9232	31
14	1,676.7836	838.8954	Lys	3,413.8122	1,707.4097	30
15	1,763.8156	882.4115	Ser	3,285.7173	1,643.3623	29
16	1,891.9106	946.4589	Lys	3,198.6852	1,599.8463	28
17	2,004.9947	1,003.0010	Leu	3,070.5903	1,535.7988	27
18	2,133.0896	1,067.0485	Lys	2,957.5062	1,479.2567	26
19	2,261.1846	1,131.0959	Lys	2,829.4112	1,415.2093	25
20	2,362.2323	1,181.6198	Thr	2,701.3163	1,351.1618	24
21	2,491.2749	1,246.1411	Glu	2,600.2686	1,300.6379	23
22	2,592.3225	1,296.6649	Thr	2,471.2260	1,236.1166	22
23	2,720.3811	1,360.6942	Gln	2,370.1783	1,185.5928	21
24	2,849.4237	1,425.2155	Glu	2,242.1197	1,121.5635	20
25	2,977.5187	1,489.2630	Lys	2,113.0772	1,057.0422	19
26	3,091.5616	1,546.2844	Asn	1,984.9822	992.9947	18
27	3,188.6144	1,594.8108	Pro	1,870.9393	935.9733	17
28	3,301.6984	1,651.3529	Leu	1,773.8865	887.4469	16
29	3,398.7512	1,699.8792	Pro	1,660.8024	830.9049	15
30	3,485.7832	1,743.3953	Ser	1,563.7497	782.3785	14
31	3,613.8782	1,807.4427	Lys	1,476.7176	738.8625	13
32	3,742.9208	1,871.9640	Glu	1,348.6227	674.8150	12
33	3,843.9685	1,922.4879	Thr	1,219.5801	610.2937	11
34	3,957.0525	1,979.0299	Ile	1,118.5324	559.7698	10
35	4,086.0951	2,043.5512	Glu	1,005.4483	503.2278	9
36	4,214.1537	2,107.5805	Gln	876.4058	438.7065	8
37	4,343.1963	2,172.1018	Glu	748.3472	374.6772	7
38	4,471.2913	2,236.1493	Lys	619.3046	310.1559	6
39	4,599.3498	2,300.1786	Gln	491.2096	246.1084	5
40	4,670.3869	2,335.6971	Ala	363.1510	182.0792	4
41	4,727.4084	2,364.2078	Gly	292.1139	146.5606	3
42	4,856.4510	2,428.7291	Glu	235.0925	118.0499	2
43	—	—	Ser	106.0499	53.5286	1

Immonium ions (low-mass markers of the residues present): Gly 30.0338, Ala 44.0495, Ser 60.0444, Pro 70.0651, Thr 74.0600, Ile 86.0964, Leu 86.0964, Asn 87.0553, Asp 88.0393, Gln 101.0709, Lys 101.1073, Glu 102.0550, Met 104.0528, Phe 120.0808.

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 6 can oxidize to the sulfoxide, which usually elutes slightly earlier in reversed-phase HPLC.
Asparagine deamidation	+0.984 Da	Asparagine at position 26 can deamidate to aspartic or isoaspartic acid through a succinimide intermediate. Moisture, higher pH and warmth speed it up.
Glutamine deamidation	+0.984 Da	Glutamine at positions 23, 36 and 39 can also deamidate, much more slowly than asparagine.
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 β4: peptide reference entry. Cosmic Peptides Research Library. Retrieved October 26, 2026, from https://cosmicpeptides.com/research/peptides/thymosin-beta-4

@misc{cosmicpeptides_research_peptides_thymosin_beta_4,
  author       = {{Cosmic Peptides}},
  title        = {Thymosin β4: peptide reference entry},
  howpublished = {Cosmic Peptides Research Library},
  year         = {2026},
  month        = oct,
  url          = {https://cosmicpeptides.com/research/peptides/thymosin-beta-4},
  urldate      = {2026-10-26},
  note         = {Last reviewed 2026-10-25}
}

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