“TB-500” is a trade name, not a sequence, and it is applied to at least two materials whose masses differ by a factor of more than five. Anyone buying it should settle which one is in the vial before anything else, and the mass spectrum settles it in one line. This page covers that check, the rest of the certificate, and what we supply in the USA.
TB-500 is a fragment, not the protein
Thymosin β4 is a 43-residue protein with an acetylated N-terminus and a mass near 4,963 Da. What is generally sold as TB-500 is a short synthetic fragment drawn from its actin-binding region — most often the acetylated heptapeptide Ac-LKKTETQ, mass near 889 Da.
Those are not variants of one compound. They are a protein and a seven-residue peptide, and almost every published result attributed to “TB-500” in secondary sources was obtained with one or the other, rarely stated. Thymosin β4 and TB-500: why the fragment is not the protein works through the distinction and how to read papers without conflating them.
The one check that settles it
Look at the measured mass on the certificate. Roughly 889 Da is the heptapeptide fragment. Roughly 4,963 Da is the full-length protein. There is no ambiguity between those two numbers and no resolution problem — any mass spectrometer that produced the report can tell them apart.
If the certificate reports no mass, or reports a mass without a calculated value to compare it against, the document has not answered the first question about the material. A supplier who cannot say which sequence they are shipping is telling you that they do not know.
What the purity figure is counting
Purity is an area percentage from HPLC: the main peak divided by the total area the detector recorded. Two things decide whether that number means much.
The first is the detection wavelength, printed on the chromatogram. At 214 nm or 220 nm the peptide bond itself absorbs, so every peptidic impurity is counted. At 280 nm only tryptophan, tyrosine and weakly phenylalanine absorb — and the Ac-LKKTETQ fragment contains none of the three. A purity figure obtained at 280 nm on this sequence is close to meaningless, because the compound and most of its impurities are nearly invisible at that wavelength. This is the single most valuable line on the document and the one most often skipped.
The second is that a short peptide resolves differently from a long one. Deletion sequences differing by a single residue are a larger relative difference in a heptapeptide than in a 43-mer, so they separate more cleanly — which means a short-peptide purity figure is generally more informative, not less. Deletion, truncation and oxidation impurities covers what each looks like, and reading an HPLC chromatogram covers what a shoulder on a main peak indicates.
What a milligram of TB-500 actually weighs
The label figure is the mass of material in the vial: peptide, plus counter-ion, plus residual water. For a peptide with two lysines the counter-ion contribution is real — TFA and acetate counter-ions covers the difference between the two salt forms. Residual water is measured by Karl Fischer titration and is commonly a few percent; water content in lyophilized peptides covers that measurement.
Net peptide content is the figure that accounts for both, and it is usually the one missing. Net peptide content explained shows how a vial can be 98% pure and 78% peptide at the same time, with both numbers honest.
On the blends
TB-500 is frequently supplied combined with BPC-157 in a single vial. A blend vial raises a question a single-component vial does not: a purity figure describes a chromatogram, and a chromatogram of two intentional components is not interpreted the same way as one of a single component. What you want from a blend certificate is the identity of each component confirmed separately and a stated composition, not one percentage.
Purity and composition in a multi-peptide blend vial covers what to ask for and how to read what comes back. BPC-157 and the limits of the published literature covers the other component.
Storage and handling
Lyophilized material is hygroscopic, and a vial opened cold collects condensation. Bring vials to room temperature before opening, close them promptly, keep them dark. Light, oxygen and temperature covers the degradation routes; weighing lyophilized peptides covers why the balance reading drifts while you are taking it. Where a vial will be entered repeatedly, aliquoting and vial entry covers limiting exposure.
What a certificate does not establish
A routine identity and purity certificate is silent on sterility, on endotoxin, and on suitability for use in a person or an animal. Those are separate tests and they were not run. Endotoxin, sterility and the limits of research grade is the longer version, and third-party versus in-house testing covers why who selected the sample changes what the report establishes.
Buying TB-500 in the USA
We ship domestically across the United States, so orders do not cross a border or go through import processing. Carrier and service are chosen at checkout — USPS, UPS or FedEx, regular or express — orders are dispatched within one business day and typical transit is two to five days.
Every certificate we hold is published in full on the certificates of analysis page, reproduced as issued rather than summarised. Certificates are not shipped with orders; vials are matched to their certificate by cap and crimp colour against the photographs on the report itself.
Sizes we supply
- TB-500 5 mg — the smaller vial, sensible where method development means repeated entries.
- TB-500 10 mg — better cost per milligram once the working quantity is established.
- BPC-157 & TB-500 blend 10 mg — both components in one vial, with the blend caveats above.
All material is supplied for laboratory research use only. It is not a drug, not a supplement, and not for use in humans or animals.
