One-electron transfer reactions of diquat radical to different reduction intermediates of oxygen. Formation of hydroxyl radical and electronically excited states.
The one-electron transfer activation of DQ++ by microsomal fractions comprises an aerobic phase and an anaerobic phase. The aerobic phase is characterized by O2 consumption, formation of electronically excited states with main emission below 600 nm, and H2O2 formation. The anaerobic phase is characterized by H2O2 consumption, DQ+ accumulation, HO. formation, and also electronically excited state formation with main emission beyond 600 nm. Superoxide dismutase abolishes the photoemission during the aerobic phase, whereas it has no effect on the photoemission originating during the anaerobic phase. The hydroxylation products of the aromatic compound salicylate, mainly 2,3- and 2,5-dihydroxybenzoic acids--indicative of the occurrence of HO.-, were detected by h.p.l.c. with oxidative electrochemical detection during the anaerobic phase, but not during the aerobic phase. Neither H2O2 consumption nor HO. are prevented by desferrioxamine. These experimental observations are interpreted on the grounds of two main electron-transfer reactions of DQ.+: under aerobic conditions, two one-electron transfer steps to molecular O2 and O2.- to yield H2O2. Under anaerobic conditions, one-electron transfer step to contaminating iron or any ferrioxamine formed to a ferrous complex which can support a Fenton-like reduction of H2O2 with formation of HO.. The toxicological relevance for the occurrence of such reactions is also discussed in terms of the formation of electronically excited states.
Mira
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D
Department of Pathology II, University of Linköping, Sweden.
Brunk
U
U
Boveris
A
A
Cadenas
E
E
D000818:Animals; D004178:Diquat / Q000378:metabolism; D004583:Electrons; D005609:Free Radicals; D006878:Hydroxides; D017665:Hydroxyl Radical; D007700:Kinetics; D008163:Luminescent Measurements; D008861:Microsomes / Q000378:metabolism; D010084:Oxidation-Reduction; D011726:Pyridinium Compounds / Q000378:metabolism; D013482:Superoxide Dismutase / Q000378:metabolism
D005609:Free Radicals; D006878:Hydroxides; D011726:Pyridinium Compounds; D017665:Hydroxyl Radical; D004178:Diquat; D013482:Superoxide Dismutase