Molecular and Cellular Radiobiology Project Title: Mechanisms of Action of Free RadicalsandHormonesRX-03-02-(c) 16. Technical Progress in FY 1973: The new EPR spectrometer (Varian E-12) along with improved ELDOR was installed and interfaced with the on-line computer system and is operative. The old EPR spectrometer, retained for high-frequency (Q-band) and continuous flow work, was upgraded through the installation of a newer model, reconditioned magnet control. A new and more successful two-stage flow/mixer was designed and fabricated for Q-band EPR experiments on free radicals involved in radiation and chemical carcinogen reactions with DNA constituents and other biochemicals, True separation of the two mixing reactions finally was achieved in a Q-band configuration. (as pointed out in other years, the Q-band apparatus significantly conserves reactants in comparison with "standard" x-band EPR flow, a critical consideration for many of our proposed applications.) Although useful, the new mixer's individual stages were slower than the best one-stage mixers, and further design improvements may be possible, Computer programs for resolution enhancement of spectra have previously been incorporated in the data system; however, for spectral lines of gaussian shape (which are common in this work) the available filter functions can provide only an approximate match, This has been satisfactory in most cases, but analysis of certain incompletely resolved spectra has been confounded by adventitious lines which are produced when spectral features are strongly sharpened by unmatched shape functions. Proper matching for gaussian lines requires Fourier transformation of either the data or the filter function, and a Fortran program incorporating modified fast Fourier transform algorithms has been written for the CDC-6600 to perform gaussian sharpening. After further modification the program can be incorporated . directly into the on-line computer system, In additional work, crystals of gamma-irradiated deoxyadenosine monohydrate (dADNS) and l-methyl thymine (1-MT) were aligned by x-ray crystallography, and x-band EPR data in many planes were taken and computer processe Some Q-band EPR studies also were carried out on 1-MT, as anticipated, An estimated 80% of the EPR measurements were carried out, and incomplete analys are in hand. These indicate temperature-sensitive radical chains in the case of 1-MT, but the hoped-for study of 1-MT (and a co-crystal of 1-MT and 9-mett -adenine) irradiated and examined at low temperature could not be accomplishec se funds for completion of a liquid-nitrogen irradiation apparatus were ailable. SGPartial analyses of several crystals of irradiated dADNS reveal multiple free radicals, one or more of which are not completely stable with tim (weeks and data from all crystals are not yet fully reconciled, Furthermcre, the single crystal spectra seem more complex than those previously published on dADNS, so final identification has not been made of those spectral components (See Continuation Sheet) 1119300 RY - 24¢