The short answer
TB stands for thymosin beta. The 500 is a development series designation carrying no chemical information. It does not denote mass, dose or sequence. The name identifies a development programme rather than describing a molecule.
Key facts
- TB
- Thymosin beta
- 500
- Development series number
- Chemical meaning of 500
- None
- Not
- Molecular weight or dose
- Actual MW
- 889.0 Da
- Systematic description
- Ac-LKKTETQ
What the parts mean
TB abbreviates thymosin beta, identifying the family the compound derives from. The 500 is a series number of the kind pharmaceutical development programmes assign, analogous to LY3437943 for retatrutide or BI 456906 for survodutide. It carries no information about the molecule.
The number that misleads
500 sits close enough to a plausible molecular weight to invite the assumption that it is one. It is not. TB-500 is 889.0 Da. Nothing about the compound is 500, not its mass, not a dose, not a residue count. The coincidence of scale is the problem.
Research material referenced
TB-500 5mg, third-party HPLC tested
Why a code name became a product name
Development codes are internal identifiers that normally disappear once a compound receives a generic name at approval. Compounds that never reach approval keep their codes, and if they acquire a market outside clinical development the code becomes the name people use. TB-500 is that pattern, and so is BPC-157.
What the name obscures
A systematic name tells you what a molecule is. TB-500 tells you which programme it came from. That is why the same name attaches to both the heptapeptide and full-length thymosin beta-4 in the market. The label describes a lineage broad enough to cover both, and nothing about it forces a distinction the chemistry requires.
Naming variants
TB-500, TB500 and TB 500 all appear, along with Thymosin Beta-4 Fragment and the sequence description Ac-LKKTETQ. Searching the sequence or the parent protein finds the science; searching the code finds the market.
Frequently asked questions
- Does 500 mean the molecular weight?
- No. TB-500 is 889.0 Da. The 500 is a development series number with no chemical meaning.
- What does TB stand for?
- Thymosin beta. The protein family the compound derives from.
Extended research context
The TB-500 (Thymosin β4 fragment) deep dive
Deep dive: TB-500 vs full-length Thymosin Beta-4
'TB-500' is a synthetic peptide corresponding to the active 17-amino-acid actin-binding region of the endogenous 43-residue Thymosin Beta-4 protein. The two are not identical. TB-500 lacks the flanking sequence that gives full-length TB-4 additional binding partners. In the research literature, papers use 'Thymosin β4' when they mean the full protein and 'TB-500' or 'AcSDKP fragment' when they mean the shorter synthetic peptide. Reading a CoA carefully to see which molecule is in the vial matters. Mass spec is the definitive check.
Actin-binding as the core mechanism
The N-terminal region of TB-4 (and TB-500 by inheritance) contains the canonical actin-binding motif. This motif sequesters G-actin monomers, modulating the G:F actin equilibrium in cell cultures. That mechanism is why almost every mechanistic paper on TB-500 traces back to cytoskeletal reorganisation, cell migration, and models of tissue repair.
Handling considerations unique to TB-500
TB-500 is a 17-residue peptide with modest amphipathicity; it reconstitutes cleanly in bacteriostatic water but is sensitive to repeated freeze/thaw. Aliquoting into single-use volumes on first reconstitution preserves potency across a batch. HPLC on the batch CoA should show a single dominant peak; a doublet suggests deamidation.
Research applications
- ▸In vitro actin-polymerisation assays (G:F actin ratio measurement)
- ▸Cell-migration and wound-scratch assays in fibroblast lines
- ▸Angiogenesis models: tube-formation and endothelial migration assays
- ▸Analytical method development for short peptides on RP-HPLC
- ▸Reference-material comparisons against endogenous Thymosin β4
Handling checklist
- ✓Store lyophilised vials at −20 °C long-term
- ✓Reconstitute with bacteriostatic water (0.9% benzyl alcohol)
- ✓Aliquot immediately to avoid freeze/thaw cycles
- ✓Refrigerate reconstituted aliquots at 2–8 °C; use within 28 days
- ✓Confirm mass (~4,963 Da for TB-500) via CoA before study use
Common research-handling mistakes
Learnt from thousands of researcher orders across our UK labs.
✗ Assuming TB-500 = full Thymosin β4
Fix: TB-500 is the 17-residue actin-binding fragment; check the CoA sequence.
✗ Repeated freeze/thaw
Fix: Aliquot at first reconstitution; each cycle degrades yield.
✗ Using tap water
Fix: Use bacteriostatic or sterile water only.
Continue researching
Peer-reviewed guides, comparators and matched reference materials.
Related questions researchers ask
Primary sources & clinical trials
Peer-reviewed research and registered trials from PubMed, ClinicalTrials.gov, PubChem, FDA and NIH. All links open in a new tab and point to the primary source, so every claim can be verified at origin.
- PubChemPubChem · TB-500 (CID 62707662)pubchem.ncbi.nlm.nih.gov
- PubMedLow TL et al., Complete amino acid sequence of bovine thymosin beta 4. PNAS 1981 (PMID 6940133)pubmed.ncbi.nlm.nih.gov
- PubMedGoldstein AL et al., Thymosin β4: a multi-functional regenerative peptide. Expert Opin Biol Ther 2012 (PMID 22074294)pubmed.ncbi.nlm.nih.gov
- PubMedShrivastava S et al., Thymosin beta4 and cardiac repair. Ann N Y Acad Sci 2010 (PMID 20536454)pubmed.ncbi.nlm.nih.gov
- PubMedSosne G et al., Thymosin beta 4 promotes corneal wound healing. Exp Eye Res 2002 (PMID 11950239)pubmed.ncbi.nlm.nih.gov
- TrialClinicalTrials.gov · Thymosin β4 (RGN-259) dry eye Phase 3 (NCT03925727)clinicaltrials.gov
- PubChemPubChem · Thymosin β4 (CID 16132341)pubchem.ncbi.nlm.nih.gov
- PubMedNIH PubMed: Thymosin beta-4 tissue repairpubmed.ncbi.nlm.nih.gov
- GuidelineGoogle: Creating helpful, reliable, people-first contentdevelopers.google.com
Written and reviewed by
The UK Peptides Editorial Team · Research library, UK Peptides
The editorial team is responsible for supplier selection, batch release decisions and the content published in this research library. Every article here is sourced to primary literature and every product page to a signed third-party certificate. Corrections are made in place and the review date updated.
More TB-500 (Thymosin β4 fragment) articles
- TB-500: Names, Spellings and What Each FindsTB-500, TB500, Tβ4, thymosin beta-4, LKKTETQ. Which term finds the science, which finds the market, and why they return different things.
- BPC-157 and TB-500 Together: What the Evidence SaysThe two are frequently combined commercially, including in blends. Whether the research literature supports studying them together is a separate question.
- TB-500 Side Effects: No Human Safety Record ExistsNo controlled human study has been published. What the rodent work reports, the concern that follows from promoting cell migration, and what is unmeasured.
- What Is TB-500? The Heptapeptide and Its Parent ProteinTB-500 is normally the acetylated heptapeptide Ac-LKKTETQ at 889 Da — not the 4,963 Da full thymosin beta-4 it derives from. The distinction matters.
- TB-500 Molecular Weight, and the Figure That Is WrongTB-500 as supplied is 889.0 Da. The widely repeated 4.9 kDa belongs to full-length thymosin beta-4 — a 5.6-fold error in any molarity calculation.
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