Table 1. Effect of additives on DNA cleavage by Na2S.
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 | 32.2 | 0.39±0.04 |
| 250 μM Na2S (Std.) | 49.8 | 0.70±0.09 |
| Std. + methanol (500 mM) | 33.1 | 0.40±0.06 |
| Std. + ethanol (500 mM) | 31.4 | 0.38±0.05 |
| Std. + mannitol (100 mM) | 32.8 | 0.40±0.04 |
| Std. + DETAPAC (10 mM) | 29.8 | 0.36±0.03 |
| Std. + SOD (100 μg/mL) | 88.2 | 2.18±0.23 |
| Std. + catalase (100 μg/mL) | 42.4 | 0.55±0.03 |