Investigation of the effects of Zn2+ and Cu2+ on the K+ transport in yeast mitochondria. Evidences for the involvement of a Zn(2+)-binding protein in the K+/H+ exchange.

Effect of Zn2+ and Cu2+ were studied on the spontaneous swelling of yeast mitochondria in potassium acetate. (i) Whatever the pH, Cu2+ stimulated the swelling. (ii) Zn2+ inhibited or stimulated the swelling depending both on pH of the medium and of its concentration: it induced an inhibition of the K+/H+ exchange at pH 6.8 and a stimulation at pH 7.7; at pH 7.4, Zn2+ inhibited the swelling at low concentration and stimulated the swelling at higher concentration. (iii) The thiol reagent mersalyl prevented the inhibition by Zn2+ whereas N-ethylmaleimide and 5,5'-dithiobis(2-nitrobenzoate) prevented the stimulation by Zn2+: this allowed to hypothesize that two distinct Zn(2+)-binding sites were involved in the inhibition and in the stimulation of the swelling of yeast mitochondria suspended in potassium acetate.