. Molecular and Cellular Radiobiology Project Title: Mechanisms of Action of Free Radicals and Hormones 17. Expected Results in FY 1974: (Cont'd,) RX-02-02-(c) oxidases in membranes will determine by EPR che incorporation of spin-label precursors (free radical "traps'' such as appropriate: nitroso compounds which can be oxidized to relatively stable nitroxide radicals in situ), Plans are also being considered to utilize non-linear EPR techniques and ELDOR to follow slow motions and possible redox reactions of spin labels incorporated in membranes both with and without stimuli for oxidative chain reactions. In studies on free radical forms of porphyrins the cation radical work and the anion radical experiments on metallotetraphenylbacteriochlorine will be completed but extension of the mapping of electron spin densities of porphyrin cation and anion radicals is planned, Certain tetramethyl- and propyl-substituted porphyrins synthesized by Adler of New England Research Institute will be studied to resolve some remaining ambiguities imanalysis and EPR splitting assignments, The use of metal isotopes with nuclear spins (Fe-57, Zn-67, Mg-25, Cd-113, etc.) remains an attractive possibility. The interesting effects of counterions on porphyrin radicals previously reported, and the relationship of these effects to heme enzyme function may be pursued further, The establishment of a conjoint Brookhaven facility for on-line EPR spectrometry during ionizing irradiation will be attempted. Nearly ten years ago Fessenden set up at Carnegie-Mellon a facility that permits EPR to be done on steady-state populations of transient free radicals produced by an electron beam from a 3-MeV Van de Graaff accelerator, This is the ' only on-line EPR/radiation equipment in the USA, save for a pulsed-radiation/ fast-EPR set-up built by Smaller at ANL which has been applied only to a - small number of special radiation problems over the last few years, yet the laboratory does not have the in-house capability to pursue more recently developed applications. Highly preductive interactions between pulse radialysis optical studies in liquids and EPR studies of irradiated single crystals or of frozen glasses and powders have led to significant advances in the understanding of radiation biophysics; and it is clear that correlations of pulse radiolysis findings with on-line EPR ofirradiated solutions would markedly accelerate this highly productive line of inquiry. New applications of radiochemical procedures and/or optical pulse radiolysis techniques to "bona fide" biochemical research (as opposed to radiochemical or radiobiological problems), especially those invol redox properties, electron transfers, and the like, including proje@€s already underway in this program could be facilitated by the cilidigeion of an on-line EPR/radiation facility. Other deparcments at Brookhaven are also interested in utilizing such a capability. Radiochemists in BNL's Chemistry Department have been using fast and slow pulse radiolysis apparatus (with the Febetron and 2-MeV Van de Graaff, respectively) in conjunction with their more ''classical" radiochemical (See Continuation Sheet) 1119305 RX-245