Two-Step Mechanism of Photodamage to Photosystem II: Step 1 Occurs at the Oxygen-Evolving Complex and Step 2 Occurs at the Photochemical Reaction Center

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• 作者：Norikazu Ohnishi ; Suleyman I. Allakhverdiev ; Shunichi Takahashi ; Shoichi Higashi ; Masakatsu Watanabe ; Yoshitaka Nishiyama ; and Norio Murata
• 刊名：Biochemistry
• 出版年：2005
• 出版时间：June 14, 2005
• 年：2005
• 卷：44
• 期：23
• 页码：8494 - 8499
• 全文大小：193K
• 年卷期：v.44,no.23(June 14, 2005)
• ISSN：1520-4995

文摘

Under strong light, photosystem II (PSII) of oxygenic photosynthetic organisms is inactivated,and this phenomenon is called photoinhibition. In a widely accepted model, photoinhibition is induced byexcess light energy, which is absorbed by chlorophyll but not utilized in photosynthesis. Usingmonochromatic light from the Okazaki Large Spectrograph and thylakoid membranes from Thermosynechococcus elongatus, we observed that UV and blue light inactivated the oxygen-evolving complexmuch faster than the photochemical reaction center of PSII. These observations suggested that the light-induced damage was associated with a UV- and blue light-absorbing center in the oxygen-evolving complexof PSII. The action spectrum of the primary event in photodamage to PSII revealed the strong effects ofUV and blue light and differed considerably from the absorption spectra of chlorophyll and thylakoidmembranes. By contrast to the photoinduced inactivation of the oxygen-evolving complex in untreatedthylakoid membranes, red light efficiently induced inactivation of the PSII reaction center in Tris-treatedthylakoid membranes, and the action spectrum resembled the absorption spectrum of chlorophyll. Ourobservations suggest that photodamage to PSII occurs in two steps. Step 1 is the light-induced inactivationof the oxygen-evolving complex. Step 2, occurring after step 1 is complete, is the inactivation of the PSIIreaction center by light absorbed by chlorophyll. We confirmed our model by illumination of untreatedthylakoid membranes with blue and UV light, which inactivated the oxygen-evolving complex, and thenwith red light, which inactivated the photochemical reaction center.