TB-500 explained: a fragment, not the full protein

Two different things are sold under the name TB-500: a short fragment and the full protein it comes from. Their masses differ many times over. This article shows what the distinction in a report depends on.

Seven residues from a protein of 43

Thymosin beta 4 is a protein of 43 building blocks. TB-500 is a section of it: the sequence Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln, or Ac-LKKTETQ for short, so seven amino acids. In the full protein this section carries the binding site for actin, which is exactly why it is studied on its own in model systems.

The leading "Ac" is not decoration. It stands for an acetyl group at the start of the chain that caps the free end. Without it this would be a different substance with a different mass.

877.99 g/mol: where the distinction lies

The molecular formula is C₃₉H₆₇N₉O₁₃, the molar mass 877.99 g/mol and the CAS number 77591-33-4. A protein of 43 building blocks weighs many times more. To check whether a report describes the fragment or the whole protein, look at the stated mass: the difference there is impossible to miss.

Mass spectrometry supplies this figure. For this substance it is the more important of the two details, because a purity figure says nothing about which molecule is pure.

Five reports, three with a purity figure

The certificate library holds five analytical reports for this substance, all from 10 mg lots, the same fill size sold here as TB-500 10 mg. Three give a numerical purity figure: lot 2024191 at 98.47%, lot 2025238 at 97.74% and Janoshik lot 237187 at 99.102%. The two reports from Liquilabs (lots 2025255 and 2025289) give none.

For the two reports without a figure, that is a gap, and it is named as such here. A report without a numerical value confirms identity and mass; it does not document a purity value. Adding a number that the report does not contain would be the worse answer.

What else to look for in a report (the method beside the value, the lot number, the date, the laboratory) is covered in How to read a certificate of analysis.

Often mentioned alongside BPC-157

TB-500 and BPC-157 appear in the same class of models and are therefore often named in the same breath. Chemically they have little in common: different origin, different length, different mass. BPC-157 explained covers the other substance in the same detail.

Both are contained together in three research blends: GLOW 70 (BPC-157, GHK-Cu and TB-500), KLOW 80 mg (BPC-157, TB-500, GHK-Cu and KPV) and BPC-157 + TB-500.

Before reconstitution

It is supplied as a lyophilised powder; what lyophilisation does to the material is covered in Storing lyophilised peptides in the laboratory. It goes into solution with bacteriostatic water, and the resulting concentration follows from the vial mass and the volume added, as described under reconstitution.

In brief

Seven amino acids with an acetyl group, 877.99 g/mol, CAS 77591-33-4, five analytical reports from the matching vial size, three of them with a purity figure (98.47%, 97.74% and 99.102%). Everything else said about this substance belongs in the scientific literature.

Questions

Is TB-500 the same as thymosin beta 4?

No. TB-500 is a section of seven amino acids from a protein of 43. The masses differ many times over, and in the analytical report the difference shows in the stated mass.

What does the "Ac" in Ac-LKKTETQ stand for?

An acetyl group at the start of the chain. It caps the free end and is part of the molecule; without it the molecular formula and mass would be different.

Which purity figures do the reports give?

Three of the five give one: 98.47%, 97.74% and 99.102%. The other two confirm identity and mass without a numerical value. That is a gap, named here rather than filled with a number added afterwards.