Molecular interference of Cd²⁺ with Photosystem II

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• 作者：Sigfridsson ; Kajsa G.V. ; Bern??t ; G??bor ; Mamedov ; Fikret ; Styring ; Stenbj??rn
• 关键词：Chl ; chlorophyll ; Cyt ; cytochrome ; DCMU ; 3-(3?????? ; 4??????-dichloro)-1 ; 1-dimethylurea ; EPR ; electron paramagnetic resonance ; F_max ; the maximal fluorescence from Q_A^aaa ; F₀ ; initial f
• 刊名：Biochimica et Biophysica Acta (BBA)/Bioenergetics
• 出版年：2004
• 出版时间：November 4, 2004
• 年：2004
• 卷：1659
• 期：1
• 页码：19-31
• 全文大小：455 K

文摘

Many heavy metals inhibit electron transfer reactions in Photosystem II (PSII). Cd²⁺ is known to exchange, with high affinity in a slow reaction, for the Ca²⁺ cofactor in the Ca/Mn cluster that constitutes the oxygen-evolving center. This results in inhibition of photosynthetic oxygen evolution. There are also indications that Cd²⁺ binds to other sites in PSII, potentially to proton channels in analogy to heavy metal binding in photosynthetic reaction centers from purple bacteria. In search for the effects of Cd²⁺-binding to those sites, we have studied how Cd²⁺ affects electron transfer reactions in PSII after short incubation times and in sites, which interact with Cd²⁺ with low affinity. Overall electron transfer and partial electron transfer were studied by a combination of EPR spectroscopy of individual redox components, flash-induced variable fluorescence and steady state oxygen evolution measurements. Several effects of Cd²⁺ were observed: (i) the amplitude of the flash-induced variable fluorescence was lost indicating that electron transfer from Y_Z to P₆₈₀⁺ was inhibited; (ii) Q_A^aaa to Q_B electron transfer was slowed down; (iii) the S₂ state multiline EPR signal was not observable; (iv) steady state oxygen evolution was inhibited in both a high-affinity and a low-affinity site; (v) the spectral shape of the EPR signal from Q_A^aaaFe²⁺ was modified but its amplitude was not sensitive to the presence of Cd²⁺. In addition, the presence of both Ca²⁺ and DCMU abolished Cd²⁺-induced effects partially and in different sites. The number of sites for Cd²⁺ binding and the possible nature of these sites are discussed.