What TB-500 is, and what it is not
Thymosin β4 is a 43-amino-acid, 4.9 kDa actin-sequestering protein present in most mammalian cells, first characterized as a thymic peptide and later shown to be a major intracellular G-actin binding protein.[1] Its actin-binding activity localizes substantially to the heptapeptide motif LKKTETQ.
TB-500 in commercial research supply is that motif, acetylated at the N-terminus and usually amidated at the C-terminus. It is around a quarter the mass of the parent protein and is synthesized rather than expressed. Suppliers that describe their TB-500 vial using thymosin β4 clinical or preclinical data are, strictly, describing a different molecule; a certificate resolves which one you are actually being sold, because the measured mass is unambiguous.

