What is TB-500?
Our records list TB-500 under CAS 885340-08-9, formula C38H68N10O14, average molecular weight 889.02, seven residues, sequence Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH. It is catalogued as thymosin beta-4 fragment (17-23), and the acetyl cap mirrors the natural acetylation of the parent.
The parent is thymosin beta-4, the 43-residue protein that is the main intracellular actin-sequestering molecule in most mammalian cells. Residues 17 to 23 are its actin-binding site, and TB-500 is the synthetic copy of that stretch. The names need separating, because full-length thymosin beta-4 carries CAS 77591-33-4 and an average mass of 4963.44 and is sometimes labelled TB-500 as well. Our vial is the heptapeptide. The clearest published definition under the name is equine doping-control chemistry (Ho, 2012). It is highly charged, very water soluble, and contains no methionine and no cysteine.
The sequence is used as an actin-regulating tool, but the evidence sits with the parent. The cell and rodent studies describing G-actin sequestration, altered migration, corneal repair and cardiac remodelling all used the 43-residue protein. The fragment's own record is thin: the analytical chemistry that defines it, plus a few reports of short LKKTET peptides retaining actin-related activity in culture. How closely the isolated segment reproduces the affinity of the intact protein is unresolved.
Reconstitution & handling
This short, highly charged sequence is among the easier in the catalog to reconstitute, and sterile or bacteriostatic water clears the cake with gentle swirling. Add the diluent against the wall and avoid shaking. Concentration is mass over diluent volume, and at 889.02 a 10 mg fill is roughly 11.2 micromoles.
Storage & stability
Keep the sealed lyophilized vial at -20 °C, desiccated and out of the light. With no methionine and no cysteine, oxidation is not the named degradation route here. The powder is hygroscopic and the carboxy-terminal glutamine is deamidation-prone in solution, so moisture exclusion and short holding times in solution are the priorities. Reconstituted stock is aliquoted for single use, held at 2 to 8 °C and not freeze-thawed.
How it's tested
Purity is determined by reversed-phase HPLC at 214 and 220 nm; with no tryptophan or tyrosine in the sequence, 280 nm detection is not informative. Identity is confirmed by mass spectrometry against the theoretical average mass of 889.02, which also separates the heptapeptide from the 4963.44 parent at a glance. Net peptide content is reported, since a short basic sequence carries a meaningful counterion load. A lot-matched certificate is on request.