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) Work by Schmidt on cytological studies on cell cycle control in collaboration with J. Van't Hof (BNL Biology Department), was undertaken to acquire proficiency in techniques that would be useful in the radiation/ carcinogenesis project. Initial research involved assessment of colchicine effects on DNA synthesis and cell cycles in root meristems of the bean Vicia faba, using tritiated thymidine autoradiographic methods. Further work during the past year showed the colchicine effects had little dependence upon the stage of the cell cycle. Therefore the emphasis shifted to sunflower (Helianthus annus) meristems synchronized by sucrose starvation. Most cells were halted in Gl with others in G2 and a few "leaking" through. Attempts were made to cause the major population in Gl to move and accumulate in G2 following a pulse of sucrose in order to verify applicability of the Principal Control Point hypothesis to G2 in this species. Initial*results were inconclusive. In collaboration with Fajer and others on free radical forms of porphyrins EPR analysis of tetraphenylbacteriochlorin cation radicals was completed following preparation of selectively deuterated derivatives by Dolphin but only after unanticipated difficulties. These stemmed from failure of certain deuteration reactions to go to completion, leaving a mixture of product free radicals following oxidation, but the complex spectra were analyzed by computer techniques. Only confirmatory experiments are now required to complete ; this phase of the work. Plans to map further the delocalization of unpaired electron density in anion radicals of porphyrins and related compounds were advanced signifi- _ cantly. Amion radicals of porphyrins, bacteriochlorins and chlorophylls were prepared coulometrically and chemically, and were examined optically and by EPR. These radicals included anions from chlorophyll, C-13-chlorophyll, bacteriochlorophylls and deuterated bacteriochlorophylls, From a comparison of their properties with those of the chemically unidentified "primary" electron acceptor components of photosynthetic organisms it was possible to rule out chlorophylls for that role in photosynthesis, Proposals to determine homogeneous rates of electron transfer between porphyrins and their radical ions by NMR line broadening and to measure magnetic susceptibilities by the Evans technique were indefinitely postponed, because of BNL's deficient NMR capabilities. The hoped-for ELDOR tions were precluded by the delayed arrival and installation of Spment, but are now imminent; and a single pilot ENDOR run during a another laboratory confirmed the applicability of that double resonafiee spectroscopy to investigations on porphyrin free radicals. Further elucidation of the pathways of electron transfer through model porphyrins was achieved in collaborative kinetic studies of Forman with (See Continuation Sheet) PE 19302 RX- 242