Fast structural changes (200-900 ns) may prepare the photosynthetic manganese complex for oxidation by the adjacent tyrosine radical

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• 作者：André ; Klauss ; Thomas Sikora ; Bjö ; rn Sü ; ss ; Holger Dau ; ^{holger.dau@fu-berlin.de}
• 关键词：chl ; chlorophyll ; ET ; electron transfer ; MES ; 2鈥恗orpholinoethane-sulfonic acid ; LIOAS ; laser-induced optoacoustic spectroscopy ; PA ; photoacoustic ; PSII ; photosystem II
• 刊名：Biochimica et Biophysica Acta (BBA)/Bioenergetics
• 出版年：2012
• 期刊代码：13_00052728
• 类别：bio
• 出版时间：August, 2012
• 卷：1817
• 期：8
• 页码：1196-1207
• 文件大小：1448 K

摘要

The Mn complex of photosystem II (PSII) cycles through 4 semi-stable states (S₀ to S₃). Laser-flash excitation of PSII in the S₂ or S₃ state induces processes with time constants around 350 ns, which have been assigned previously to energetic relaxation of the oxidized tyrosine (Y_Z^ox). Herein we report monitoring of these processes in the time domain of hundreds of nanoseconds by photoacoustic (or 鈥榦ptoacoustic鈥? experiments involving pressure-wave detection after excitation of PSII membrane particles by ns-laser flashes. We find that specifically for excitation of PSII in the S₂ state, nuclear rearrangements are induced which amount to a contraction of PSII by at least 30 脜³ (time constant of 350 ns at 25 掳C; activation energy of 285 +/鈭?#xA0;50 meV). In the S₃ state, the 350-ns-contraction is about 5 times smaller whereas in S₀ and S₁, no volume changes are detectable in this time domain. It is proposed that the classical S₂ = > S₃ transition of the Mn complex is a multi-step process. The first step after Y_Z^ox formation involves a fast nuclear rearrangement of the Mn complex and its protein-water environment (~ 350 ns), which may serve a dual role: (1) The Mn鈥?complex entity is prepared for the subsequent proton removal and electron transfer by formation of an intermediate state of specific (but still unknown) atomic structure. (2) Formation of the structural intermediate is associated (necessarily) with energetic relaxation and thus stabilization of Y_Z^ox so that energy losses by charge recombination with the Q_A^{鈭?/sup> anion radical are minimized. The intermediate formed within about 350 ns after Y_Zox formation in the S₂-state is discussed in the context of two recent models of the S₂ = > S₃ transition of the water oxidation cycle. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: From Natural to Artificial.}