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Fragment identity and research record · Updated October 13, 2026
The TB-500 peptide is a seven-amino-acid fragment, Ac-LKKTETQ, from residues 17 to 23 of thymosin beta 4, a 43-residue protein. The two are different molecules with separate registry entries. As of October 2026, the human trials described below are registered under the parent protein, and TB-500 is sold only as a research compound.
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TB-500 is Ac-LKKTETQ, seven amino acids taken from the 43-residue thymosin beta 4 sequence.
FDA's substance registry gives the fragment and the parent protein different identifiers.
RGN-352, a thymosin beta 4 trial, was withdrawn before it started and enrolled no one.
A TB-500 certificate of analysis should confirm which molecule is present before it reports purity.
The FDA substance registry entry lists TB-500 under identifier QHK6Z47GTG. It describes an acetylated piece of thymosin beta 4 that covers residues 17 to 23. The sequence is Ac-LKKTETQ, made by chemical synthesis. As of October 2026 no regulator has approved it as a medicine, and in the United States it is supplied as a research chemical for laboratory work.
The name causes trouble because people apply it to two things. Some vendor listings describe the seven-residue fragment at about 889 g/mol. Others describe a full-length sequence near 4,963 g/mol under the same label. The fragment and parent identity guide sets out how to tell the two apart.
Thymosin beta 4 is a 43-residue protein that binds G-actin and takes part in cytoskeletal remodeling. TB-500 reproduces a short segment of that sequence. The two share seven residues, yet the fragment is a separate molecule with its own record.
TB-500 has seven amino acids, and thymosin beta 4 has 43.
Vendor listings give about 889 g/mol for the fragment and about 4,963 g/mol for the full sequence.
FDA's registry uses QHK6Z47GTG for TB-500 and 549LM7U24W for thymosin beta 4.
When reading a paper, check which molecule the authors used. A study of thymosin beta 4 describes the full protein in the model it used. It makes no automatic claim about Ac-LKKTETQ, so each result should be matched to the exact molecule used.
Most published work concerns the full protein. Cell and animal studies on thymosin beta 4 have looked at actin binding, cell migration, cytoskeleton organization, skin and corneal models, heart biology, inflammation and progenitor cells. Each finding applies to the molecule and model that team used.
A 2024 study by Rahaman and colleagues in the Journal of Chromatography B measured TB-500 and its metabolites in enzyme systems, human serum and rat samples, then compared their activity in a fibroblast wound assay. Only Ac-LKKTE showed significant wound-healing activity against the control in that assay. The finding concerns one metabolite in an in vitro model; it does not establish a clinical effect of Ac-LKKTETQ.
The registry entries discussed here are filed under "Thymosin Beta 4" instead of TB-500, and their substance descriptions name full-length or recombinant material. Two entries are covered below.
RegeneRx registered RGN-352 as an injectable form of thymosin beta 4 for acute myocardial infarction. The ClinicalTrials.gov record NCT01311518 shows it as withdrawn, and gives the reason as a trial that never started. Enrollment is zero, so the entry holds no participant data.
Beijing Northland Biotech ran a Phase IIa trial of injectable recombinant human thymosin beta 4. Registry record NCT05485818 lists it as completed on November 18, 2021. This is another parent-protein program, and it does not involve the fragment either.
Neither of these records studies Ac-LKKTETQ. A registry listing should be checked against its substance description and study text before it is treated as human evidence. The MOTS-c registry guide shows how to check a registry sponsor.
The peptide COA reading guide explains lot matching and the identity-purity distinction. Check the current TB-500 lot through the lot report lookup before relying on a product description.
For the TB-500 peptide, a certificate has to settle identity before purity. An HPLC percentage describes how clean a sample is. It cannot show whether the sample holds the short fragment or the full-length parent. A report should show:
the lot number it covers, matching the lot you hold
the name of the issuing laboratory and a report identifier
mass spectrometry data that agree with Ac-LKKTETQ rather than the full sequence
HPLC purity with its chromatogram, not a bare percentage
an endotoxin result, where the laboratory provides one
The 5mg TB-500 product page lists material for laboratory research in the Peptide Fragments & Blends category. Check the identity result and lot-matched certificate before comparing the listing with a study.
No. TB-500 is the seven-residue acetylated fragment Ac-LKKTETQ, covering residues 17 to 23 of thymosin beta 4, which has 43 residues. FDA's substance registry lists them under different identifiers. Research on the parent protein does not automatically apply to the fragment, so a paper or certificate should name the exact molecule it covers, as of October 2026.
The two parent-protein studies cited here concern thymosin beta 4, not the Ac-LKKTETQ fragment. Those records do not establish a completed human trial of TB-500. This is the finding from the cited records checked October 13, 2026, rather than a claim about every possible registry or publication.
RegeneRx registered RGN-352 as an injectable thymosin beta 4 study for acute myocardial infarction. ClinicalTrials.gov lists it as NCT01311518, withdrawn, with the reason given as a trial that never started. No participants enrolled, so the entry holds no results and says nothing about the TB-500 fragment either way.
The report should carry the lot number of the material it covers, name the issuing laboratory, and confirm identity by mass spectrometry as Ac-LKKTETQ before it reports HPLC purity. An endotoxin result is useful where the laboratory offers one.
Browse the current research catalogue and check the lot documents in the COA library. Catalogue materials are supplied for research use only, not human or veterinary use.