Evidence that cytochrome b{sub 559} protects photosystem II against photoinhibition
- Univ. of Illinois, Urbana, IL (United States)
Light that exceeds the photosynthetic capacity of a plant can impair the ability of photosystem II to oxidize water. The light-induced inhibition is initiated by inopportune electron transport reactions that create damaging redox states. There is evidence that secondary electron transport pathways within the photosystem II reaction center can protect against potentially damaging redox states. Experiments using thylakoid membranes poised at different ambient redox potentials demonstrate that light-induced damage to photosystem II can be controlled by a redox component within the reaction center. The rate of photoinhibition is slow when the redox component is oxidized, but increases by more than 10-fold when the redox. component is reduced. Here, using spinach thylakoid membranes, we provide evidence that the redox component is cytochrome b{sub 559}, an intrinsic heme protein of the photosystem II reaction center. The results support a model in which the low-potential (LP) form of cytochrome b{sub 559} protects photosystem II by deactivating a rarely formed, but hazardous redox state of photosystem II, namely, P680/Pheo{sup -}/Q{sub A}{sup -}. Cytochrome b{sub 559}LP is proposed to deactivate this potentially lethal redox state by accepting electrons from reduced pheophytin.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 245322
- Journal Information:
- Biochemistry (Eaton), Journal Name: Biochemistry (Eaton) Journal Issue: 34 Vol. 34; ISSN 0006-2960; ISSN BICHAW
- Country of Publication:
- United States
- Language:
- English
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