Semin Boris K, Seibert Michael
BioEnergy Sciences & Technology Directorate, National Renewable Energy Laboratory, Golden, CO, 80401, USA.
Department of Biophysics, Faculty of Biology, Lomonosov Moscow State University, 119234, Moscow, Russia.
J Bioenerg Biomembr. 2016 Jun;48(3):227-40. doi: 10.1007/s10863-016-9651-2. Epub 2016 Feb 4.
We have investigated the interaction of Fe(II) cations with Ca-depleted PSII membranes (PSII[-Ca,4Mn]) in the dark and found that Fe(II) incubation removes 2 of 4 Mn ions from the tetranuclear Mn cluster of the photosynthetic O2-evolving complex (OEC). The reduction of Mn ions in PSII(-Ca,4Mn) by Fe(II) and the concomitant release of two Mn(II) cations is accompanied by the binding of newly generated Fe(III) in at least one vacated Mn site. Flash-induced chlorophyll (Chl) fluorescence yield measurements of this new 2Mn/nFe cluster (PSII[-Ca,2Mn,nFe]) show that charge recombination in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) occurs between Qa (-) and the remaining Mn/Fe cluster (but not YZ (●)) in the OEC, and extraction of 2 Mn occurs uniformly in all PSII complexes. No O2 evolution is observed, but the heteronuclear metal cluster in PSII(-Ca,2Mn,nFe) samples is still able to supply electrons for reduction of the exogenous electron acceptor, 2,6-dichlorophrenolindophenol, by photooxidizing water and producing H2O2 in the absence of an exogenous donor as seen previously with PSII(-Ca,4Mn). Selective extraction of Mn or Fe cations from the 2Mn/nFe heteronuclear cluster demonstrates that the high-affinity Mn-binding site is occupied by one of the iron cations. It is notable that partial water-oxidation function still occurs when only two Mn cations are present in the PSII OEC.
我们研究了Fe(II)阳离子在黑暗中与缺钙的光系统II（PSII）膜（PSII[-Ca,4Mn]）的相互作用，发现Fe(II)孵育从光合放氧复合体（OEC）的四核锰簇中去除了4个锰离子中的2个。Fe(II)对PSII(-Ca,4Mn)中锰离子的还原以及随之而来的两个Mn(II)阳离子的释放伴随着新生成的Fe(III)在至少一个空出的锰位点上的结合。对这种新的2Mn/nFe簇（PSII[-Ca,2Mn,nFe]）进行闪光诱导叶绿素（Chl）荧光产率测量表明，在存在3-(3,4-二氯苯基)-1,1-二甲基脲（DCMU）的情况下，电荷复合发生在Qa(-)与OEC中剩余的Mn/Fe簇（而非YZ(●)）之间，并且2个锰的提取在所有PSII复合物中均匀发生。未观察到氧气释放，但PSII(-Ca,2Mn,nFe)样品中的异核金属簇仍能够通过光氧化水并在没有外源供体的情况下产生H2O2，为外源电子受体2,6-二氯酚靛酚的还原提供电子，这与之前在PSII(-Ca,4Mn)中观察到的情况相同。从2Mn/nFe异核簇中选择性提取Mn或Fe阳离子表明，高亲和力的锰结合位点被其中一个铁阳离子占据。值得注意的是，当PSII OEC中仅存在两个锰阳离子时，部分水氧化功能仍然会发生。
