Effects of arsenite, hydrogen peroxide, or NONOate on the zinc content of purified PARP-1. PARP-1 protein was isolated from untreated HaCat cells by immunoprecipitation, then the isolated PARP-1 was treated with sodium arsenite (50 μM), hydrogen peroxide (50 μM), and NONOate (20 μM) for 48 hrs at 4°C The zinc content in the isolated PARP-1 was detected spectrophotometrically (DU 800, Beckman Coulter). Data were presented as means ± S.D., * P<0.05 vs. control group; n=6.