Distribution and biological activity ofβ-thymosins.

β-Thymosins, a group of highly homologous peptides consisting of about 40 amino acid residues, were found to be distributed from mammals up to echinoderms. Althogh they have first been isolated from mammalian thymus tissue preparations, their occurrance is not organ-specific and they are present even in different types of cells. For thymosinβ 4 several biological activities have been reported, stating that this peptide acts as a thymus peptide hormone and is also involved in the neuroendocrine and immune system. However, it was recently demonstrated that thymosinβ 4 has actin-sequestering properties and therefore might play an important role in the regulation of the microfilament system. This fact gives a new outlook on the real biological function ofβ-thymosins.