 isolated nuclei from mammalian cells contain a calcium - dependent endonuclease . 
 the produced dna fragmentation is a necessary step in the sequence of events resulting in apoptosis ( programmed cell death ) . 
 we report here that zinc and cadmium inhibit the calcium - dependent endonuclease . 
 the essential metal ion zinc may counterbalance the calcium - mediated apoptosis . 
 in contrast to zinc , cadmium alone stimulates the endonuclease by replacing calcium . 
 thus cadmium exerts a dual effect : micromolar concentrations inhibit the apoptotic endonuclease in the presence but activate the enzyme in the absence of calcium.imagesfigure 2 . 
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