Contribution of zinc and other metals to the biological activity of the serum thymic factor.

TLDR

FTS loses biological activity after chelation with the metal‑ion chelator Chelex 100. FTS activation occurs when a metal, particularly Zn, binds to the peptide, as confirmed by atomic absorption spectrometry. Adding Zn salts restores FTS activity, with a 1:1 metal‑to‑peptide ratio being optimal, revealing two forms—an inactive Zn‑free form and an active Zn‑bound form called thymulin (FTS‑Zn).

Abstract

The serum thymic factor (FTS) utilized in its synthetic or natural form loses its biological activity in a rosette assay after treatment with a metal ion-chelating agent, Chelex 100. This activity is restored by the addition of Zn salts and, to a lesser extent, certain other metal salts. FTS activation is secondary to the binding of the metal to the peptide. The metal-to-peptide molar ratio of 1:1 provides the best activation. These data indicate the existence of two forms of FTS. The first one lacks Zn and is biologically inactive; the second one contains Zn and is biologically active, for which we propose the name of "thymulin" (FTS-Zn). The presence of Zn in synthetic FTS was confirmed by atomic absorption spectrometry. The interaction between Zn and FTS was further suggested by microanalysis demonstrating the presence of this metal in thymic reticuloepithelial cells.