Effects of electron donor and acceptors, electron transfer mediators, and superoxide dismutase on lipid peroxidation in illuminated chloroplast fragments

Effects of artificial electron donor and acceptors, electrontransfer mediators, and superoxide dismutase on lipid peroxidationin illuminated chloroplast fragments were studied. An indicator of lipid peroxidation, malondialdehyde (MDA) formation,was stimulated by 3-(3,4-dichlorophenyl)-l,l-dimethylurea (DCMU).The DCMU stimulated MDA formation was inhibited about 90% byreduced 2,6-dichloroindophenol (DCIP). In photosystem I-enrichedparticles, MDA formation was larger than that in normal chloroplastfragments on the chlorophyll basis. Benzyl viologen and ferredoxinstimulated DMA formation. Superoxide dismutase inhibited MDAformation strongly in the presence of benzyl viologen and weaklyin its absence; the enzyme sometimes stimulated MDA formationin the presence of ferredoxin. Carbonylcyanide m-chlorophenylhydrazone(CCCP) stimulated MDA formation and maximal stimulation wasattained at about 20 µM CCCP.Phenazine methosulfate, DCIPand benzoquinone inhibited MDA formation in the presence andabsence of CCCP. From the above results, we confirmed our previous conclusionthat most of the singlet molecular oxygen formed in illuminatedchloroplasts is generated by electron transfer from O_2^–to oxidized electron transfer components located on the oxidizingsides of photosystems I and II. (Received September 3, 1975; )