Semin B K, Davletshina L N, Aleksandrov A Yu, Lanchinskaya V Yu, Novakova A A, Ivanov I I
Faculty of Biology, Lomonosov Moscow State University, Moscow 119899, Russia.
Biochemistry (Mosc). 2004 Mar;69(3):331-9. doi: 10.1023/b:biry.0000022066.38297.8a.
Light-induced interaction of Fe(II) cations with the donor side of Mn-depleted photosystem II (PS II(-Mn)) results in the binding of iron cations and blocking of the high-affinity (HAZ) Mn-binding site. The pH dependence of the blocking was measured using the diphenylcarbazide/2,6-dichlorophenolindophenol test. The curve of the pH dependence is bell-shaped with pK1 = 5.8 and pK2 = 8.0. The pH dependence of the O2-evolution mediated by PS II membranes is also bell-shaped (pK2 = 7.6). The pH dependence of the process of electron donation from exogenous donors in PS II(-Mn) was studied to determine the location of the alkaline pH sensitive site of the electron transport chain. The data of the study showed that the decrease in the iron cation binding efficiency at pH > 7.0 during blocking was determined by the donor side of the PS II(-Mn). Mössbauer spectroscopy revealed that incubation of PS II(-Mn) membranes in a buffer solution containing 57Fe(II) + 57Fe(III) was accompanied by binding only Fe(III) cations. The pH dependence of the nonspecific Fe(III) cation binding is also described by the same bell-shaped curve with pK2 = 8.1. The treatment of the PS II(-Mn) membranes with the histidine modifier diethylpyrocarbonate resulted in an increase in the iron binding strength at alkaline pH. It is suggested that blocking efficiency at alkaline pH is determined by competition between OH- and histidine ligand for Fe(III). Because the high-affinity Mn-binding site contains no histidine residue, this fact can be regarded as evidence that histidine is located at another (other than high-affinity) Fe(III) binding site. In other words, this means that the blockage of the high-affinity Mn-binding site is determined by at least two iron cations. We assume that inactivation of oxygen-evolving complex and inhibition of photoactivation in the alkaline pH region are also determined by competition between OH- and a histidine residue involved in coordination of manganese cation outside the high-affinity site.
光诱导的Fe(II)阳离子与缺锰光系统II（PS II(-Mn)）供体侧的相互作用导致铁阳离子的结合以及高亲和力（HAZ）锰结合位点的阻断。使用二苯卡巴肼/2,6-二氯酚靛酚试验测量了阻断的pH依赖性。pH依赖性曲线呈钟形，pK1 = 5.8，pK2 = 8.0。PS II膜介导的O2释放的pH依赖性也是钟形的（pK2 = 7.6）。研究了PS II(-Mn)中外源供体电子供体过程的pH依赖性，以确定电子传输链碱性pH敏感位点的位置。研究数据表明，在阻断过程中，pH > 7.0时铁阳离子结合效率的降低是由PS II(-Mn)的供体侧决定的。穆斯堡尔光谱显示，PS II(-Mn)膜在含有57Fe(II) + 57Fe(III)的缓冲溶液中孵育时，仅伴有Fe(III)阳离子的结合。非特异性Fe(III)阳离子结合的pH依赖性也由相同的钟形曲线描述（pK2 = 8.1）。用组氨酸修饰剂焦碳酸二乙酯处理PS II(-Mn)膜会导致碱性pH下铁结合强度增加。有人认为，碱性pH下的阻断效率由OH-和组氨酸配体对Fe(III)的竞争决定。由于高亲和力锰结合位点不含组氨酸残基，这一事实可被视为组氨酸位于另一个（除高亲和力之外的）Fe(III)结合位点的证据。换句话说，这意味着高亲和力锰结合位点的阻断至少由两个铁阳离子决定。我们假设，在碱性pH区域中放氧复合体的失活和光激活的抑制也由OH-与参与高亲和力位点外锰阳离子配位的组氨酸残基之间的竞争决定。
