TB-500 (TB500, thymosin beta-4 fragment) Research Peptide

What is TB-500?

TB-500, sometimes written TB500 and often just called the thymosin beta-4 fragment, is a synthetic seven-residue peptide with the sequence Ac-LKKTETQ: an N-terminally acetylated copy of residues 17 through 23 of thymosin beta-4. Thymosin beta-4 itself is a small, highly conserved protein found in nearly every mammalian cell type, first characterized in Allan Goldstein’s thymus-extract work and later recognized as the main intracellular protein that holds monomeric actin in reserve. The fragment we sell strips that parent protein down to the stretch that does the actin binding.

Nobody owns TB-500 the way a pharmaceutical company owns a branded drug. It came out of academic peptide chemistry and is now produced by contract synthesis under CAS 885340-08-9. Researchers order it because the short sequence is far easier to synthesize, characterize and dissolve than the full-length protein, and because much of the cell-migration and wound-model literature on thymosin beta-4 points back to this motif as the part that matters. Our TB-500 comes in a single 10mg size, tested at the lot level, with the certificate on the product page at /product/tb-500/.

Structure and mechanism

The sequence LKKTET is the actin-binding motif of thymosin beta-4, and TB-500 is that motif plus one flanking glutamine with an acetyl cap on the N-terminus. In the full protein this stretch sits in the middle of an otherwise fairly unstructured chain, and it’s the part that docks onto monomeric G-actin, keeping it from polymerizing into filaments until the cell needs it. Since actin turnover underlies almost every kind of cell movement, the proposed mechanism is that the peptide changes how readily cells reorganize their cytoskeleton, migrate and spread.

Published cell-culture work with the parent protein and with the fragment has looked at endothelial cell migration, keratinocyte movement and the assembly of capillary-like tubes on matrix gels. There’s also a line of work from Bock-Marquette and colleagues tying thymosin beta-4 to integrin-linked kinase signalling in cardiac cells, though how much of that carries over to the seven-residue fragment is less settled. Our honest read: the actin interaction is well established for the motif, the downstream cellular effects are documented for the full protein, and fragment-specific mechanism data is thinner than the marketing suggests. A short, linear, unmodified peptide like this has no receptor in the classical sense, so questions about selectivity or agonism don’t apply the way they do for BPC-157 or a GLP-1 analogue.

What the published research covers

Most of what’s in print is on thymosin beta-4 rather than on TB-500 specifically, so anyone planning a study should read the methods sections closely to see which molecule was actually used. The preclinical literature clusters around a few areas. Dermal wound models in rodents, starting with Malinda’s 1999 paper, looked at closure and re-epithelialization after topical or systemic application of the protein. Corneal epithelial models followed, largely from Sosne’s group, along with cardiac injury studies in mice after the 2004 Nature paper on cardiac cell migration and survival. Other groups have examined the fragment or the protein in tendon explants, hair follicle models and inflammatory readouts.

On the clinical side, RegeneRx ran early-phase human trials of full-length thymosin beta-4 in dermal and ophthalmic wound settings. Those are published as trial reports and belong to the literature on the whole protein; the seven-residue fragment has no equivalent trial record that we’re aware of. If you’re weighing this fragment against another tissue-repair peptide for a study design, the BPC-157 vs TB-500 page walks through the differences side by side.

Reconstitution and handling

The vial arrives as a lyophilized white cake or powder under a crimped stopper. Before you open anything, let it come to room temperature so you don’t pull condensation into the vial when the septum is pierced. Reconstitute with bacteriostatic water, adding it slowly down the inside wall of the vial instead of jetting it straight onto the cake. The peptide is short and goes into solution readily, so a gentle swirl is all it needs. Don’t shake it; foaming and vigorous agitation introduce aggregation and lose material to the glass and the air interface.

Keep sterile technique throughout, since bacteriostatic water slows microbial growth but doesn’t sterilize a contaminated solution. Once it’s dissolved, label the vial with the compound name, the lot number from the COA, the date of reconstitution and the concentration you made, so the next person in the lab isn’t guessing. The volume of diluent depends on the concentration your assay calls for, and that’s a study-design decision we leave to you.

Storage and stability

Sealed and lyophilized, TB-500 should sit at -20C, protected from light, in the original vial with the stopper intact. The dry cake is far more forgiving than a solution. Once reconstituted, keep it at 2-8C in the refrigerator and plan on using it within 28 days; after that, hydrolysis and adsorption to the container start to erode what the COA measured.

Avoid repeated freeze-thaw on the solution. Each pass through the freezing point concentrates solutes as ice forms and can drive aggregation, and repeated passes are a common reason a reconstituted vial stops behaving the way it did in the first week. If your study needs the solution over a longer period, aliquot it once into single-use volumes and thaw each only once. Keep it out of strong light and away from the fridge door. We ship the lyophilized vial at ambient temperature because the dry state tolerates a few days of transit; the cold-chain requirement starts when water goes in. Orders process within 1 business day, and every vial is vialed, finished, tested and shipped in the USA.

How it’s tested

Every lot of TB-500 we stock goes through the same three-part routine: HPLC purity, mass spectrometry identity and bacterial endotoxin, by a named third-party lab, with the lot COA on the product page. HPLC tells you what fraction of the UV-absorbing material elutes as the main peak, and our specification is >99% purity. Mass spectrometry confirms that the main peak has the mass expected for Ac-LKKTETQ and isn’t a deletion sequence or an unacetylated variant, which is the failure mode HPLC alone can miss on a peptide this short. The endotoxin assay catches bacterial contamination carried over from synthesis or fill.

When you read a certificate, look for the lot number matching the label on your vial, the observed mass sitting within the instrument’s tolerance of the theoretical mass, a purity figure with the chromatogram actually attached, and a named lab with a report date. We keep current and past certificates in the library at /coas/ so you can check a lot after the product page has moved on to a newer one. If a certificate doesn’t line up with your own assay, tell us.