Molecular and Cellular Radiobiology Project Title: Mechanisms of Action of Free Radicals and Hormones 14. Scope: (Cont'd.) RX-03-02-(c) of radiobiological or biochemical interest during electron beam irradiation, contingent upon development of a BNL interdepartmental EPR/irradiation facility. Free radical forms of porphyrins appear to be important intermediates in some of the redox reactions of heme enzymes. Closely related chlorin and bacteriochlorin free radicals are involved in the photochemical steps of photosynthesis. One project evaluates the significance of porphyrin radicals in biological electron transport collaboration with J. Fajer (BNL Department of Applied Science), R. H. Felton (Georgia Tech.) and D. Dolphin (Harvard). This work is crucial to the BNL free radical program in establishing a firm theoretical and experimental basis for free radical research. ~ Another project is directed at the nature of free radical signals intrinsic to tissue or those induced by carcinogens, pollutants, drugs, disease or radiation. Since 1954 undefined and unidentified EPR signals have been obtained from "surviving" (fresh but not actively metabolizing) tissues, These signals are believed to represent paramagnetic complexes containing three components: 1) nitrogen oxide-like moieties from the xenobiotic (i.e., exogenous) molecules or their metabolites, 2) sulfur ligands from endogenous biological sites (quite possibly ferredoxin-like electron acceptors in cellular drug and aryl hydrocarbon mixed-function oxidase systems)., and 3) iron atoms from the P-450 or P-448 cytochrome enzymes in the oxidase systems, Thus the EPR spectrum obtained from tissues during the latent period‘ of chemical carcinogenesis may not reflect the neoplastic process but the metabolism of a cellular "defense reaction" against the carcinogenic agent. Non-neoplastic drugs may be inducers of tissue mixed-function oxidase enzymes and may give rise to these EPR signals. Special apparatus was developed at BNL to identify the paramagnetic sites in surviving tissues which give rise to the "normal" singlet-type EPR signals. Further development of these procedures, plus supplementation with computer processing of data and with ELDOR and ENDOR spectrometry is planned. If identification of tissue paramagnetic sites is attained correlation with exposure to pollutants, different disease states, particular drug therapies, and the effects of ionizing radiations will start, ELDOR and ENDOR are complementary not competitive double resonance copies for amplification of EPR in research on free radicals and other tic centers, Some of the unresolved or incompletely analyzed spectra watudied by ELDOR and ENDOR, Recent achievement of ENDOR capability Ks underscores the need for ENDOR equipment if BNL is to remain compet ttive. Free radical reactions associated with enzyme and hormone actions will be aimed at investigation of some enzymic and pyridine nucleotide free radicals (See Continuation Sheet) 1119298 RX-238