Effects of transition metals on TRH-receptor interaction.

The interaction of TRH receptors and metal ions was investigated. Although the addition of a physiological serum concentration (20 microM) of Zn2+ or Cu2+ to the TRH radioreceptor assay reaction mixture significantly increased the binding capacity, pretreatment of crude synaptic membranes with Ni2+, Zn2+, Cu2+ or Pd2+ resulted in a significant loss of binding activity. The receptor preparation was bound to [3H]TRH in the presence of 10 mM Ni2+ and was solubilized by Triton X-100. Gel filtration was carried out with cold Tris-HCl-Triton buffer without Ni2+. The molecular weight of the solubilized TRH-macromolecular complex was about 300,000 daltons, and Ni2+ was found in the same fraction as the solubilized TRH-receptor. These results suggest that metal ions have inverse effects in different steps of TRH-receptor interaction and that a TRH-receptor molecule indicates a Ni-binding molecule.