What is TB-500's CAS number?

The heptapeptide has no widely used CAS of its own; it is PubChem CID 62707662. CAS 77591-33-4 belongs to the parent protein, thymosin beta-4.

Is a listing quoting 77591-33-4 wrong?

It is describing thymosin beta-4's registration. Whether it is wrong depends on what is in the vial, which is why the sequence and mass fields matter more.

Which field on a certificate should I trust?

The measured mass and the stated sequence. A CAS number is transcribed; a mass is measured.

TB-500 CAS Number and Chemical Identity

The short answer

CAS 77591-33-4 is thymosin beta-4's registry number, not TB-500's. TB-500 as the acetylated heptapeptide is PubChem CID 62707662 at 889.0 Da. Material is routinely listed under the parent's CAS, which merges two compounds differing by more than 4 kDa.

Key facts

CAS 77591-33-4: Thymosin beta-4 (the parent protein)
Tβ4 PubChem CID: 16132341, 4,963 Da
TB-500 PubChem CID: 62707662, 889.0 Da
LKKTETQ CID: 10169788, 847.0 Da
Sequence: Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln
Practical check: Mass spectrometry (889 vs 4,963)

Which identifier belongs to which compound

CAS 77591-33-4 resolves to PubChem CID 16132341: C212H350N56O78S, 4,963 Da, forty-three residues. That is thymosin beta-4. TB-500 as the heptapeptide sits at CID 62707662, C38H68N10O14, 889.0 Da. These are separate registrations for separate substances, and quoting the first for the second is not a technicality.

Why the merge happens

TB-500 is a development code rather than a chemical name, so it has no natural identifier of its own in the way a systematic name does. Suppliers and databases reach for the parent protein's CAS because it is the recognised registry entry associated with the name. The practice is understandable and it produces listings where the CAS, the molecular weight and the described sequence do not describe the same molecule.

Research material referenced

TB-500 5mg, third-party HPLC tested

Buy TB-500 · £23.99

Reading a certificate properly

The sequence is the most informative field. Seven residues, LKKTETQ, means the heptapeptide regardless of what CAS appears at the top. Forty-three residues means full-length thymosin beta-4. If a certificate states a mass near 889 alongside a CAS of 77591-33-4, the document is internally inconsistent and the mass is the field to trust, because it is measured rather than transcribed.

Confirming identity analytically

Mass spectrometry against the theoretical value. There is no ambiguity between 889 and 4,963 on any instrument. The sequence contains no cysteine and no methionine, so the disulfide and +16 Da oxidation satellites common on other peptide spectra should not appear; their presence would indicate something other than the stated compound.

Confirming purity

Reverse-phase HPLC against truncated and deletion sequences. Seven residues is a short synthesis and purity is typically high, so a low figure warrants explanation. Note that full-length thymosin beta-4 at 43 residues is a far harder synthesis with correspondingly more opportunity for deletion sequences, another reason the two products are not interchangeable in practice.

Frequently asked questions

What is TB-500's CAS number?: The heptapeptide has no widely used CAS of its own; it is PubChem CID 62707662. CAS 77591-33-4 belongs to the parent protein, thymosin beta-4.
Is a listing quoting 77591-33-4 wrong?: It is describing thymosin beta-4's registration. Whether it is wrong depends on what is in the vial, which is why the sequence and mass fields matter more.
Which field on a certificate should I trust?: The measured mass and the stated sequence. A CAS number is transcribed; a mass is measured.

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.

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.

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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.

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