FIGURE 6.

Arsenite decreases the zinc content and DNA binding of PARP-1 isolated from cells. A–C, cells were treated with arsenite (As) or TPEN, and the indicated proteins were isolated by immunoprecipitation as described under “Experimental Procedures.” A, cells were treated with the indicated concentrations of arsenite for 40 h or with 5 μm TPEN for 24 h, PARP-1 was immunoprecipitated, and zinc content was measured as described under “Experimental Procedures.” Values are normalized to the untreated control and represent the mean ± S.D. of three independent experiments. *, p < 0.05. B, cells were treated as described for A, and PARP-1 DNA binding was measured by EMSA as described under “Experimental Procedures.” C, shown is the quantification of data in B based on densitometry. The concentration of zinc in the culture medium was 1.5 μm, so at the highest arsenite concentration, the molar ratio of arsenite to zinc in the tissue culture medium was 1.33:1.0. Values represent the mean ± S.D. of three independent experiments. *, p < 0.05.