RESUMEN
Zn(7)- and Cd(7)-metallothioneins were prepared. Mitochondria were isolated from rat hearts. Mitochondria lipid fluidity, protein conformation and mobility were determined by using ESR spin label. Ca(2+)-Mg(2+)-ATPase activity and (45)Ca uptake activity were assayed. It was found that, after being damaged by hydroxyl radicals, mitochondria lipid fluidity and protein mobility decreased, protein conformation changed and mitochondria Ca(2+)-Mg(2+)-ATPase activity, (45)Ca uptake activity were inhibited. Both Zn(7)- and Cd(7)-metallothioneins could antagonize hydroxyl radicals and protect myocardial mitochondria. However, this effect of Zn(7)-metallothionein was stronger than that of Cd(7)-metallothionein, because the apo-metallothionein has about 10 000 fold higher affinity for Cd than for Zn, so, Zn(7)-metallothionein would release more Zn(2+). More reduced thiol groups would be revealed.