Molecular and Cellular Radiobiology Project Title: Mechanisms of Action of Free Radicals and Hormones 16, Technical Progress in FY 1973: (Cont'd.) RX-03-02-(c) due to free radicals from the sugar (deoxyribose)moiety. Nevertheless, there is already further support for last year's proposal that resolution enhancement of EPR "powder spectra’ might provide identification of sugar radicals in sample configurations of more general radiobiophysical use than the single crystal, Computer-enhanced spectra from irradiated polycrystalline dADNS were equivalent to those obtained from crushing an irradiated single crystal, and pending final confirmation upon complete analysis of the single crystal, the dominant EPR features of a sugar radical are now assignable in the resolution-enhanced powder spectra. Radiomimetic chemical reactions wherein the hydroxyl radical is produced by chemical reduction of peroxide were studied further, using the Q-band flow systems. Most experiments continued to use Ti(III) \ds the initiating reductant, but the proposal to evaluate the faster Cr(I1I)/H202 reaccion was commenced, using 6-methyl uracil as the test substrate, Preliminary results indicated some improvement over Ti(III)/H907 reactions, but the system proved combersome and time-consuming, so reaction conditions were not optimized and further explorations were postponed in light of the limited time left available for Schmidt and the uncertainty of his replacement. However, with the Ti(III) system much of the work anticipated last year was carried forward, The first reports of EPR spectra from hydroxyl radical reactions on bases and nucleosides of nucleic acid purines were further refined. Sugar and base radicals are evident from purine nucleosides. Halogenated base: give rise to markedly different spectra, Adenine derivatives deuterated at" C8 and run in deuterated solvent revealed only slight line narrowing, indicatir little unpaired electron delocalization on carbon atoms with dissociable protons or on C8 (this last finding contrasts with significant C8 interaction in hydrogen-addition radicals of adenine compounds, as previously reported). Toward the year's end the expected completion and testing of the new two-stage flow/mixer for Q-band EPR allowed a study om transient free radicals from carcinogens and pollutants and their reactions with DNA consticuencts and other biological target molecules. A detailed EPR spectrum was obtained by dithionite reduction of the carcinogen 4-nitroquinoline-l-oxide (4-NQO) and it strongly resembled that reported by Nagata from ultraviolet irradiation of the more proximate carcinogen form, 4-hydroxyaminoquinoline-1oxide. Although reaction of the radical with one-electron oxidants was obsgrved, no reaction was detected with reductants or with nucleic acid const. ts. Hence this free radical does not react in the fashion expected f ultimate carcinogen. This is not surprising in view of the present u Patanding that electrophilic forms of carcinogens (such as certain epoxideq or catimic free radicals) form adducts at nucleophilic sites of nucleic acids, because the radical obtained from 4-NQO by dithionite reduction was electron-rich, so any carcinogenic radical that might be obtained from 4-NQO derivatives would have to be a different form. (See Continuation Sheet) [119301 RX- 241