Hub · Peptide Quality & Verification
TB-500 vs thymosin beta-4: is TB-500 the same molecule?
TB-500 is not the same molecule as thymosin beta-4, a natural protein 43 amino acids long (amino acids are the small units proteins are built from; Low et al., 1981). In the papers that define it, TB-500 is a synthetic fragment (a short piece of that chain, made in a laboratory): the seven amino acids LKKTETQ with an acetyl group, a small chemical tag, on the first one (Ho et al., 2012).
01Same molecule?Contents
Your cells keep their shape with an inner scaffold of thread-like protein, and the threads are built from a protein called actin. UniProt, a public protein database, records thymosin beta-4 as a binder of single actin units (UniProt P62328), and a 2010 review calls it the major actin-sequestering molecule in cells with a nucleus, meaning it holds actin units in reserve (Sosne et al., 2010).
This page is part of the peptide quality & verification hub, where a peptide means a short chain of amino acids. It asks one naming question: when someone writes TB-500, which molecule is meant? Research papers that give an exact amino-acid sequence, the order of units along a chain, answer it.
Key facts
| Parent protein | Thymosin beta-4, 43 amino acids long (Low et al., 1981) |
|---|---|
| TB-500 as defined in two papers | Ac-LKKTETQ, where Ac- is the acetyl tag; 7 amino acids (Ho et al., 2012; Esposito et al., 2012) |
| Fragment position | Positions 17 to 23 of the 43 (Sosne et al., 2010) |
| Protein record | UniProt P62328, an entry in a public protein database |
| Evidence used here | Identity and sequence findings only; no effect findings used |
Is TB-500 the same as thymosin beta-4?
TB-500 is not the same as thymosin beta-4 in the papers that define the two. Thymosin beta-4 is a protein of 43 amino acids (Low et al., 1981), and each letter in its sequence stands for one unit of the chain. Two laboratory-testing papers define TB-500 as the seven-unit peptide Ac-LKKTETQ, positions 17 to 23 of that protein, with an acetyl group added to its first unit (Esposito et al., 2012; Ho et al., 2012). A fragment is a short piece of a longer molecule, so TB-500 is a piece of thymosin beta-4, not the whole protein.
What is full-length thymosin beta-4?
Thymosin beta-4 is a natural protein of 43 amino acids, sequenced from calf thymus, a small gland in the chest, in 1981 (Low et al., 1981). UniProt lists the human sequence, in groups of ten letters, as SDKPDMAEIE KFDKSKLKKT ETQEKNPLPS KETIEQEKQA GES, leaving out the starting amino acid, methionine, which the cell removes, and records an acetylated serine, an amino acid, at the first position (UniProt P62328). The same entry says the protein binds and sequesters actin monomers, meaning it holds single actin units and stops them joining into threads. A 2010 review names the stretch LKKTETQ, at positions 17 to 23, as the central actin-binding part of the protein (Sosne et al., 2010).
Because the sequence is a string of letters, it reads like a sentence. The first four letters, SDKP, form a different named part, Ac-SDKP, which TB-500 does not include (Sosne et al., 2010).
What is the TB-500 fragment, and how do papers identify it?
A 2012 paper on testing horse samples describes TB-500 as a veterinary preparation, a product made for animal use, whose key ingredient is LKKTETQ with an artificial acetyl group on its first end (Ho et al., 2012). A second 2012 paper detected Ac-LKKTETQ inside TB-500 by high-performance liquid chromatography with high-resolution mass spectrometry, a method that separates a mixture and weighs each molecule, and it also made the fragment by chemical synthesis (Esposito et al., 2012). In both papers the name TB-500 is tied to a stated sequence and a stated acetyl tag, which is what makes the identity checkable.
The name alone does not settle identity; the letters and the tag are what a laboratory can test. The TB-500 research guide collects the published studies in one place.
Evidence limits
Does the name TB-500 always mean this exact fragment?
No source on this page shows that every product or study called TB-500 contains Ac-LKKTETQ. Ho et al. (2012) and Esposito et al. (2012) each name the sequence and the acetyl tag for the material they examined, which is evidence about those preparations only. A 2003 animal study abstract names the seven-unit peptide LKKTETQ and does not say whether it carried an acetyl tag (Philp et al., 2003), so that abstract alone cannot be matched to Ac-LKKTETQ. A label, a catalogue name or a paper that says TB-500 without the sequence and the tag leaves the identity open.
A researcher holding paperwork can ask whether a batch record names the sequence and the tag. How to read a certificate of analysis covers the fields, and what a batch or lot number lets a researcher verify covers the code tying a vial to its record. The catalogue entry is TB-500 reference material.
Comparison
Each row compares one checkable property. Every cell names its source, and no row describes effects.
| Property | Thymosin beta-4 (full length) | TB-500 (as defined in the papers) |
|---|---|---|
| Length | 43 amino acids (Low et al., 1981) | 7 amino acids (Ho et al., 2012) |
| Position | Positions 1 to 43 (Sosne et al., 2010) | Positions 17 to 23 of the 43 (Ho et al., 2012) |
| Sequence in one-letter codes (one letter per amino acid) | SDKPDMAEIE KFDKSKLKKT ETQEKNPLPS KETIEQEKQA GES (UniProt P62328) | LKKTETQ (Ho et al., 2012) |
| Acetyl tag | On the first unit, serine (Low et al., 1981; UniProt P62328) | On the first unit, the amino acid leucine, added artificially (Ho et al., 2012) |
| Origin | Natural protein, sequenced from calf thymus (Low et al., 1981) | Synthetic version of the fragment (Ho et al., 2012) |
| First four positions | Hold the named part Ac-SDKP (Sosne et al., 2010) | Lie outside the fragment, which spans positions 17 to 23 (Ho et al., 2012) |
FAQ
Is TB-500 a fragment of thymosin beta-4?
TB-500 is described as a fragment of thymosin beta-4: the seven-amino-acid stretch at positions 17 to 23, with an added acetyl tag (Ho et al., 2012; Sosne et al., 2010).
Is thymosin beta-4 the same as Ac-SDKP?
Thymosin beta-4 is not the same as Ac-SDKP. Ac-SDKP is a four-amino-acid part at positions 1 to 4 of the protein, and UniProt lists it as a peptide contained in thymosin beta-4 (Sosne et al., 2010; UniProt P62328). TB-500 covers positions 17 to 23 and does not include it (Ho et al., 2012).
Does Australian law list TB-500 and thymosin beta-4 as the same thing?
Australian law lists them separately. The Poisons Standard, the national list of controlled medicines and poisons, names TB-500 and thymosin beta 4 (thymosin β4) as two entries, each in Schedule 4 (prescription-only medicines) and Appendix D, clause 5 (poisons that must not be possessed without authority), in the Therapeutic Goods (Poisons Standard—October 2026) Instrument 2026, F2026L01327, checked 1 October 2026 UTC (universal time). Each entry is a name without a description.
Part of
Peptide Quality & VerificationHow research peptide material is tested, what a certificate of analysis actually records, and how a buyer checks that a vial matches its paperwork. Every article in this hub is about verification, not about use.
Citations
5 sourcesLow TL, Hu SK, Goldstein AL. Proceedings of the National Academy of Sciences. 1981;78(2):1162-1166.
doi:10.1073/pnas.78.2.1162Sosne G, Qiu P, Goldstein AL, Wheater M. FASEB Journal. 2010;24(7):2144-2151.
doi:10.1096/fj.09-142307Ho EN, Kwok WH, Lau MY, Wong AS, Wan TS, Lam KK, Schiff PJ, Stewart BD. Journal of Chromatography A. 2012;1265:57-69.
doi:10.1016/j.chroma.2012.09.043Esposito S, Deventer K, Goeman J, Van der Eycken J, Van Eenoo P. Drug Testing and Analysis. 2012;4(9):733-738.
doi:10.1002/dta.1402Philp D, Badamchian M, Scheremeta B, Nguyen M, Goldstein AL, Kleinman HK. Wound Repair and Regeneration. 2003;11(1):19-24.
doi:10.1046/j.1524-475x.2003.11105.x
Form Laboratories supplies research-use-only reference material. This article is an educational summary of published third-party literature. It is not medical advice, not a use instruction, and research material is not for human or animal use.