Table 2. Cleavage of plasmid DNA by H2S in the presence of various concentrations of iron(III).
Strand cleavage assays were performed as described in the Experimental Section. Briefly, supercoiled double-stranded plasmid DNA (pGL2-Basic, 1 μL of a 1 mg/mL solution in 10 mM Tris-HCl, 1 mM EDTA, pH 7.5) was added to water (17 μL), followed by addition of sodium sulfide nonahydrate (2 μL in sodium phosphate, pH 7, 500 mM). Form I and II plasmid DNA were resolved on an agarose gel and stained with ethidium bromide. The DNA was visualized by UV-transillumination and the amounts measured by digital image analysis. The number of single strand breaks per plasmid DNA molecule (S) was calculated using the equation S = −ln f1 where f1 is the fraction of plasmid present as form I.97
| Reaction/Additive | % Nicked, Form II DNA | S-valueb |
|---|---|---|
| DNA Alone | 33.9 | 0.40±0.05 |
| 250 μM Na2S alone (Std.) | 48.2 | 0.60±0.04 |
| Std. + FeSO4 (1 nM) | 53.7 | 0.80±0.14 |
| Std. + FeSO4 (100 nM) | 66.3 | 1.01±0.06 |
| Std. + FeSO4 (1 μM) | 83.9 | 1.83±0.04 |
| FeSO4 alone (1 μM) | 32.1 | 0.36±0.07 |