Table 3. Cleavage of plasmid DNA by H2S oxidation products.
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 | 31.8 | 0.33±0.02 |
| 500 μM Na2S | 43.2 | 0.56±0.08 |
| 1 mM Na2S | 46.3 | 0.63±0.12 |
| 500 μM NaS2O3 | 27.8 | 0.30±0.02 |
| 1 mM NaS2O3 | 28.1 | 0.30±0.02 |
| 500 μM Na2SO3 | 28.3 | 0.31±0.04 |
| 1 mM Na2SO3 | 27.8 | 0.29±0.03 |
| 500 μM Na2SO4 | 23.7 | 0.23±0.02 |
| 1 mM Na2SO4 | 24.7 | 0.23±0.04 |
| 500 μM NaHSO3 | 29.8 | 0.28±0.00 |
| 1 mM NaHSO3 | 31.4 | 0.31±0.03 |