, Volume 81, Issue 1, pp 41-47

Superoxide, Hydrogen Peroxide and Hydroxyl Radical in D1/D2/cytochrome b-559 Photosystem II Reaction Center Complex

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Spin-trapping electron spin resonance (ESR) was used to monitor the formation of superoxide and hydroxyl radicals in D1/D2/cytochrome b-559 Photosystem II reaction center (PS II RC) Complex. When the PS II RC complex was strongly illuminated, superoxide was detected in the presence of ubiquinone. SOD activity was detected in the PS II RC complex. A primary product of superoxide, hydrogen peroxide, resulted in the production of the most destructive reactive oxygen species, •OH, in illuminated PS II RC complex. The contributions of ubiquinone, SOD and H2O2 to the photobleaching of pigments and protein photodamage in the PS II RC complex were further studied. Ubiquinone protected the PS II RC complex from photodamage and, interestingly, extrinsic SOD promoted this damage. All these results suggest that PS II RC is an active site for the generation of superoxide and its derivatives, and this process protects organisms during strong illumination, probably by inhibiting more harmful ROS, such as singlet oxygen.

This revised version was published online in October 2005 with corrections to the Cover Date.