Guide
TB-500 vs TB-500 fragment 17-23
A 43-residue peptide and the seven residues inside it that do the actin binding. Masses, and why the fragment weighs a seventh as much.
Published September 4, 2026
One is a 43-residue peptide. The other is seven residues taken from inside it.
| Peptide | Vial sizes | From |
|---|---|---|
| TB-500 (TB4) | 5mg, 10mg | $34.99 CAD |
| TB-500 Frag 17-23 | Single size | $59.99 CAD |
| BPC157 + TB500 Blend | 5mg + 5mg, 10mg + 10mg | $64.99 CAD |
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The parent and the piece
Thymosin beta-4 is a 43-residue peptide. TB-500 is the synthetic version of its active region, supplied as the acetylated form.
Within that sequence, residues 17 to 23 form the actin-binding domain: LKKTETQ. That short stretch is what the fragment is. It carries the actin-binding activity of the parent and nothing else the parent does.
Studying the fragment isolates one variable. Studying the full peptide keeps everything in play. Neither is better; they answer different questions.
The numbers
| Residues | Formula | Molecular weight | CAS | |
|---|---|---|---|---|
| TB-500 | Full active region | C212H350N56O78S | 4963.44 g/mol | 77591-33-4 |
| Fragment 17-23 | 7 (LKKTETQ) | C31H55N9O11 | 729.83 g/mol | Not published |
The fragment is 14.7% of the parent's mass. A mass-spec result cannot confuse the two, and no report should.
Seven times the molecules
This is where the molar column earns its keep. A 5 mg vial of TB-500 is about 1 micromole. A 5 mg vial of the fragment is about 6.9. Same label, seven times the molecules.
| Vial | 1 mL | 2 mL | 3 mL | 5 mL |
|---|---|---|---|---|
| 5 mg | 5 mg/mL1.01 mM | 2.5 mg/mL0.504 mM | 1.67 mg/mL0.336 mM | 1 mg/mL0.201 mM |
| 10 mg | 10 mg/mL2.01 mM | 5 mg/mL1.01 mM | 3.33 mg/mL0.672 mM | 2 mg/mL0.403 mM |
TB-500 (TB4) vial sizes we sell, at four diluent volumes. Molarity uses 4963.44 g/mol. Other volumes
If you are working in molar units and you swap one for the other at the same mass concentration, you have changed the experiment by a factor of seven. The calculator has a preset page for each.
In blends
TB-500, not the fragment, is what appears in our blends: the BPC-157 + TB-500 blend, GLOW and KLOW. BPC-157 vs TB-500 covers the other half of that pairing.
The one number to remember
4,963 g/mol is the full peptide. 730 is the seven-residue actin-binding piece. Per milligram the fragment gives you seven times the molecules.
For research use only. Not for human or animal consumption.
Frequently asked questions
What is TB-500 fragment 17-23?
+
Residues 17 to 23 of thymosin beta-4, the seven-residue stretch that carries the actin-binding activity. Its sequence is LKKTETQ and it weighs 729.83 g/mol against 4,963.44 for the full peptide.
Is the fragment the same as TB-500?
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No. It is a short piece of it. A fragment carries one activity of the parent molecule and none of the rest, which is exactly why it is studied separately.
Why use a fragment instead of the whole peptide?
+
To isolate one variable. If the question is about actin binding, the fragment tests that without the other 36 residues contributing anything. That is a research design decision, not a quality difference.
Do they reconstitute differently?
+
The technique is identical. The molar numbers are not: 5 mg of the fragment is about seven times as many molecules as 5 mg of the full peptide.
Related articles
- Where to buy a peptide blend in CanadaPeptide blends are sold in Canada as research chemicals. What a blend vial holds, how to reconstitute one, and how to check what is inside it.
- DSIP in Canada: what's sold and how to check itDSIP is sold in Canada as a research chemical for lab use. Vial sizes, prices, how the rules apply, and how to check that a vial is really DSIP.
- KLOW vs KPV: a four-peptide blend and a tripeptideKLOW contains KPV as one of its four peptides, so they are not alternatives. What separates an 80 mg blend vial from a 10 mg KPV vial, and how each is checked.
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