Conversion of the spin state of the manganese complex in photosystem II induced by near-infrared light
Conversion of the spin state of the manganese complex in photosystem II induced by near-infrared light
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DOI：
10.1021/bi960636w
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发表时间：
1996-06-04
期刊：
影响因子：
2.9
通讯作者：
Rutherford, AW
中科院分区：
文献类型：
--
作者：
Boussac, A;Girerd, JJ;Rutherford, AW
负责光系统II中水氧化的锰配合物(Mn-4)在S-2状态下可被EPR检测到，该状态是酶循环的五个氧化还原状态之一。在10K下，可以观察到S-2态作为多线信号(自旋1/2)或g=4.1时的信号(自旋3/2或自旋5/2)。结果表明，在150K左右，红外光吸收时，多线信号的能态转变为g=4.1信号的能态，这种转换在200K时是完全可逆的。这种转换的作用光谱在820 nm(12200 cm(-1))处有极大值，类似于二钼氧杂环((MnIV)-Mn-III)模型体系中的价态电荷转移带。我们认为，多线信号到g=4.1信号的转换是由Mn团簇自身对红外光的吸收所致。从而导致从Mn-III到Mn-IV的电子转移。因此，g=4.1信号仅根据其价态分布的这种变化而从与引起多线信号的状态不同的状态产生。在重组光系统II的S-2态和去钙光系统中观察到了近红外光效应。早期文献中的结果表明，g=4.1态是由130K的光照优先形成的，这是两个光化学事件的结果：第一个是光合作用电荷分离导致的S-2态，从而产生多线信号；第二个是由于在给定的宽带照明中同时和无意地存在820 nm光，这个态转变为g=4.1态。因此，没有理由认为对g=4.1信号负责的状态是引起多行信号的状态的先兆。
The manganese complex (Mn-4) which is responsible For water oxidation in photosystem II is EPR detectable in the S-2 state, one of the five redox states of the enzyme cycle. The S-2 State is observable at 10 K either as a multiline signal (spin 1/2) or as a signal at g = 4.1 (spin 3/2 or spin 5/2). It is shown here that at around 150 K the state responsible for the multiline signal is converted to that responsible for the g = 4.1 signal upon the absorption of infrared light, This conversion is fully reversible at 200 K. The action spectrum of this conversion has its maximum at 820 nm (12 200 cm(-1)) and is similar to the intervalence charge transfer band in di-mu-oxo-((MnMnIV)-Mn-III) model systems, It is suggested that the conversion of the multiline signal to the g = 4.1 signal results from absorption of infrared light by the Mn cluster itself, resulting in electron transfer from Mn-III to Mn-IV. The g = 4.1 signal is thus proposed to arise from a state which differs from that which gives rise to the multiline signal only in terms of this change in its valence distribution. The near-infrared light effect was observed in the S-2 state Of Sr2+-reconstituted photosystem II and in Ca2+-depleted, EGTA (or citrate-)-treated photosystem II but not in ammonia-treated photosystem II. Earlier results in the literature which showed that the g = 4.1 state was preferentially formed by illumination at 130 K are reinterpreted as being the result of two photochemical events: the first being photosynthetic charge separation resulting in an S-2 State which gives rise to the multiline signal and the second being the conversion of this state to the g = 4.1 state due to the simultaneous and inadvertent presence of 820 nm light in the broad-band illumination given. There is therefore no reason to consider the state responsible for the g = 4.1 signal as a precursor of that which gives rise to the multiline signal.