LIGHT‐INDUCED FORMATION OF O‐2˙ OXYGEN RADICALS IN SYSTEMS CONTAINING CHLOROPHYLL
- 1 December 1980
- journal article
- Published by Wiley in Photochemistry and Photobiology
- Vol. 32 (6) , 793-798
- https://doi.org/10.1111/j.1751-1097.1980.tb04057.x
Abstract
—: It has been shown recently that photosystem 1 particles, photosystem 1 lipid vesicles and chlorophyll‐a lipid vesicles show identical photochemical reactions in the presence of oxygen e.g. H+‐and O2‐uptake (Van Ginkel, 1979). Therefore, spin‐trapping experiments were done to identify the oxygen radicals formed. The spintrap phenyltertiarybutylnitrone (PBN) failed to yield information about oxygen radicals.With the spintrap 5,5‐dimethyl‐1‐pyrroline‐1‐oxide (DMPO), however, we obtained a mixed spectrum of O‐2˙ and OH·‐adducts generated in chloroplasts, photosystem 1 particles or chlorophyll‐a lipid vesicles. These data indicate that chlorophyll‐a in an artificial membrane can also catalyze O‐2˙‐formation. Chlorophyll‐a lipid vesicles catalyze light‐induced formation of the Tiron‐semiquinone free radical, which has been proposed as a specific O‐2˙‐probe (Greenstock and Miller, 1975). However, OH· scavengers strongly reduce the formation of this radical, whereas superoxide dismutase does not.Pulse‐radiolysis measurements showed that the rate constant for the reaction of Tiron with OH· is 8.2 · 109M‐1 s‐1, which is considerably higher than the published Tiron/O‐2˙ rate constants. Therefore, Tiron is a better spin probe for OH· than for O‐2˙.We suggest that light‐induced H+‐and O‐2˙‐uptake in membranes containing chlorophyll‐a in the presence of ascorbate is caused mainly by the very rapid reaction of OH· with ascorbate.This publication has 31 references indexed in Scilit:
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