Radiation chemical studies of sensitization by 5-bromouridine-5′-monophosphate (5-BrUMP)

Summary This study was undertaken to investigate the mechanism of chemical radiosensitization by halogenated bases incorporated into DNA. Radiation-induced base and sugar-phosphate backbone damage to 5-bromouridine-5-monophosphate (5-BrUMP) was monitored using a flow system connected in series with a recording spectrophotometer, a bromide (Br^–)-specific ion analyzer and a Technicon auto-sampler. The system was used to assay loss of UV-absorbing 5,6 double-bond, release of Br^– and inorganic phosphate (Pi) release using an automated colorimetric method, as a function of gamma-ray dose. Results obtained with radical scavengers indicate that, unlike non-halogenated nucleotides where the hydroxyl radical (· OH) is the principal damaging species, 5-BrUMP is damaged by the hydrated electron (e _aq ^– ), hydrogen atom (H·) and · OH, producing a high yield of base damage and Br^– and Pi release in anoxia. Another novel feature of 5-BrUMP radiolysis is that oxygen, by convertinge _aq ^– and H· to the unreactive superoxide radical anion (0 ₂ ^– ), has a protective effect on both base and phosphate ester damage. Under · OH-scavenging conditions, where the radiation yield of reductive debromination is 3.8, there is some Pi release, suggesting the possibility of intramolecular hydrogen atom transfer from the sugar ring to the 5-uracilyl radical and subsequent sugar-phosphate bond cleavage. This hypothesis is supported by the action of oxygen and thiols in modifying thee _aq ^– -mediated sugar-phosphate damage.     

Induction of Plant Pyridoxine (Pyridoxamine) 5′-Phosphate Oxidase Activity by Light

Botrytis cinerea, which was isolated from the surface of stored sunflower seed, produced a novel biologically active natural product when cultured on shredded wheat medium. The metabolite, trivially named cinereain, was a ruby red crystalline product with the molecular formula C₁₈H₂₁N₃O₃ and melting point 201~203°C. The structure was unequivocally established by single crystal X-ray diffraction; UV, IR, NMR (¹H and ¹³C) and mass spectrometry supported the crystallographic data. Cinereain significantly inhibited the growth of etiolated wheat. coleoptiles (p < 0.01) at 10^-3 and 10^-4 m in bioassays. No effects were noted on treated intact greenhousegrown bean and tobacco plants, but there was mild necrosis and chlorosis in corn.