期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1992
卷号：89
期号：17
页码：7929-7933
DOI：10.1073/pnas.89.17.7929
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Photosystem II reaction centers in plants, algae, and cyanobacteria are susceptible to damage by excess light that irreversibly impairs activity and eventually results in the proteolytic degradation of at least one of the core proteins. The sequence of events and underlying molecular mechanisms that lead to photoinhibition are poorly understood. Here we present evidence for a one-electron redox component that exerts strong control over the rate of photosystem II photoinhibition in isolated thylakoid membranes. Monitoring the impact of various doses of visible light on the rate of water oxidation and on the variable chlorophyll fluorescence, we found that reduction of the redox component increased the rate of photoinhibition >15-fold. Anaerobic potentiometric titrations of the rate of photoinhibition revealed a redox component with a midpoint potential near 20 mV at pH 7.5. The titrations fit a Nernst equation for a one-electron reaction and were nearly pH independent. Although we have not yet identified the chemical species being titrated, a likely candidate is lowpotential cytochrome b-559. We believe this observation reveals an electron transfer pathway in photosystem II that functions to protect the reaction center against excess light energy.
