Aging Aging

8-oxoguanine Levels in Nuclear DNA 177Fig. 2. ECD and UV traces for rat liver nuclear DNA with a typically low backgroundlevel of 8-oxo-dG.and 8-oxo-dG have an absorbance of 13AU (254 nm) and 12.3AU (245 nm),respectively. Standard curves are run on each day, with dG at 50, 100, and 150 mMand 8-oxo-dG at 0.25, 0.5, 1, and 2 nM.4. Do not leave samples for longer than 12 h at 5°C in the autosampler; there issome evidence of oxidation after this time.5. Check for carryover of 8-oxo-dG by inserting a 0.25 nM 8-oxo-dG standard aftereach set of quadruplicate samples. Check that the peak area is constant throughoutthe run.6. The concentration of dG is estimated from the UV peak; 8-oxo-dG from the electrochemicalsignal at 400 mV. Results are usually expressed as the number ofresidues of 8-oxo-dG per 10 5 dG.4. Notes1. As DF is light sensitive, cover tubes with foil, keep lid on water bath, etc. AlsoDF is unstable at room temperature and 4°C, so the solid and buffers containingDF should be stored at –20°C. The buffers should be freshly thawed before useand surplus discarded.2. Do not attempt to economize by refreezing working solutions of enzymes andsaving them for use at a later date. Be ruthless and discard unused solutions.AcknowledgmentsWe are grateful for financial support from the Ministry of Agriculture, Fisheriesand Food and the Scottish Office Agriculture, Environment and FisheriesDepartment.