DESCRIPTION: The long-term objective of this work is to understand how oxygen radicals damage DNA and thus destroy the genetic integrity of the cell, and to learn how the cell responds to such stress. Genetic, biochemical and now chemical studies have shown that toxicity by H2O2, O2.-, O2 may arise largely through iron- mediated Fenton reactions that generate oxyradicals that resemble, but are not identical to, diffusible hydroxyl radicals, and that DNA is perhaps the major target of these radicals. In essence, Fe+2 reacts with H2O2 to form the damaging radical and Fe+3, then NADH reduces the Fe+3 back to Fe+2. The goals during the next grant period will be I) to study further the role(s) of NAD(P)H in these processes in vivo and in vitro; II) to understand the basis of sequence preferences for DNA damage by iron and peroxide and how iron interacts with DNA with some emphasis upon telomeres; III) to study the role of O2 in Fe/H2O2/DNA chemistry; IV) to complete inventories of DNA base damage during these processes; and V) to study levels of oxidative damage in mitochondrial DNA in steady state and H2O2-stress conditions. It is the contention of the principal investigator that these studies should help to clarify the basis of degenerative and other disease states brought about by oxygen radicals, and also help to design regimens to treat and prevent such disease processes.