What TB-500 is
TB-500, also written TB500 and often searched as "TB-500 peptide", is the name commonly given to a short synthetic fragment of thymosin beta-4, a 43-residue protein that is abundant in most mammalian cells and is the main intracellular sequestering agent for monomeric actin. The fragment we supply is residues 17 to 23 of that protein, Leu-Lys-Lys-Thr-Glu-Thr-Gln, with an acetyl group on the N-terminus to match the acetylated N-terminus of the parent protein. This heptapeptide contains the LKKTET motif that is responsible for binding actin, and it is the segment most often studied when the question is which part of thymosin beta-4 accounts for a given observation.
The name has also been applied, in the grey market and in some older literature, to the full-length 43-residue protein. The two are very different molecules: the fragment has an average molecular weight of approximately 889 g/mol, while the full protein is close to 4,963 g/mol. We supply the fragment, and the LC-MS result on every certificate makes the distinction unambiguous. The CAS number for the acetylated heptapeptide is 885340-08-9.
The published literature on the compound, with references, is collected in the monograph.
What you receive
Each vial contains TB-500 as a white lyophilised powder, sealed with a flip-off cap over a crimped stopper, in the net quantity stated on the label: 5 mg or 10 mg. There is no carrier, mannitol or other excipient unless the batch certificate says otherwise. The batch number is printed on the label and matches the certificate in our register.
Reading the certificate for a TB-500 batch
Purity by reversed-phase HPLC is reported as the area of the main peak against all peaks and should be above 99% for a heptapeptide. Identity by LC-MS is reported as the observed mass against the expected mass of about 889 Da. This single number answers the most important question about any product sold under this name, since a mass of several thousand daltons would mean the vial contains the full-length protein, and a mass 42 daltons lower than expected would mean the N-acetyl group is missing. Net peptide content gives the milligrams of peptide actually present after allowing for water and counter-ions.
The impurities seen with this fragment are usually deletion sequences and a trace of the deacetylated form, both of which elute close to the main peak. At the sub-1% level these are normal. Our guide to reading a certificate of analysis shows annotated examples, and HPLC and LC-MS explained describes the methods.
Storage and handling
Sealed vials should be kept refrigerated at 2 to 8 °C and protected from light; −20 °C is preferable for storage beyond a few months, and the lyophilised powder is stable for well over a year under those conditions. The heptapeptide is hydrophilic and modestly hygroscopic, so allow the vial to reach room temperature before opening. It dissolves readily in water, saline or bacteriostatic water at neutral pH. Solutions are best prepared fresh or aliquoted and frozen; the storage and stability guide covers solvents, concentrations and aliquoting.