Cadmium and zinc mediated changes of the Ca(2+)-dependent endonuclease in apoptosis

Isolated nuclei from mammalian cells contain a Ca(2+)-dependent endonuclease [1]. The produced DNA fragmentation is a necessary step in the sequence of events resulting in apoptosis [2]. We report here that zinc inhibits the DNA fragmentation in dependence of the free Ca2+ concentrations, suggesting that a balance between zinc and calcium might regulate the Ca(2+)-dependent endonuclease. Incubation of nuclei with different free calcium concentrations combined with cadmium shows a stronger inhibition of the DNA fragmentation than zinc. Cadmium inhibits the endonuclease in a calcium-independent way. Surprisingly cadmium alone is able to stimulate the endonuclease, thus to replace Ca2+.