Probing the reactivity of the zinc and cadmium ions bound to rabbit liver metallothioneins with EDTA.

Abstract

Reactions of native and reconstituted rabbit liver metallothioneins (MT's) with excess EDTA at pH 7 were studied by 1H NMR, electronic absorption and atomic absorption spectroscopy. There was a reasonable agreement between the amounts of Zn2+ and Cd2+ removed as determined by the various methods. Specific structural changes accompanying metal removal were observable by NMR. Most of the Zn2+ in Zn7-MT, reacted rapidly with EDTA. One to two g-ions of Zn2+ in native Cd,Zn-MT's were labile, but none of the Cd2+ was extracted rapidly by EDTA. The cadmium protein Cd7-MT1, reconstituted via the low pH-apothionein method, appeared to contain EDTA-reactive Cd2+ bound in a different manner to either Zn2+ or Cd2+ in the native protein.