Mechanism of photosystem II photoinactivation and D1 protein degradation at low light: The role of back electron flow
Mechanism of photosystem II photoinactivation and D1 protein degradation at low light: The role of back electron flow
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DOI：
10.1073/pnas.94.4.1579
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发表时间：
1997-02-18
影响因子：
11.1
通讯作者：
Ohad, I
中科院分区：
文献类型：
--
作者：
Keren, N;Berg, A;Ohad, I
限制电子流的光强度可诱导光系统II（PSII）反应中心D1蛋白的快速降解，这种现象的机制尚不清楚，我们认为在低激发速率下，电子流和Q（B）（. -）或Q（A）（. -）半醌受体和PSII供体侧的氧化S-2，S-3状态可通过产生活性氧物质引起氧化损伤，因此，每个光化学事件的损伤应随着PSII激发速率的降低而增加。为了验证这一假设，单次转换闪光之间的暗间隔对水氧化失活，电荷分离和重组的影响，在菠菜类囊体中测定了PS Ⅱ和D1蛋白的降解，每次闪光的PS Ⅱ失活随着闪光之间的黑暗间隔的增加而增加，并且在黑暗间隔处达到平台，允许Q（B）（. -）/ S-2、S-3或Q（A）（. -）/ S-2国家（分别约为200和40 s），在这些激发速率下：（i）每次闪光分别使0.7%和0.4%的PSII失活，并且使0.4%和0.2%的D1蛋白降解，并且（ii）每次闪光的损伤比过量连续光递送的等量能量诱导的损伤高约2个数量级，这些结果表明，在活性PSII中的电荷重组是由低速率的激发促进的，并且可以解释限制光诱导的DI蛋白的快速周转的高量子效率。
Light intensities that limit electron flow induce rapid degradation of the photosystem II (PSII) reaction center D1 protein, The mechanism of this phenomenon is not known, We propose that at low excitation rates back electron flow and charge recombination between the Q(B)(.-) or Q(A)(.-) semiquinone accepters and the oxidized S-2,S-3 states of the PSII donor side may cause oxidative damage via generation of active oxygen species, Therefore, damage per photochemical event should increase with decreasing rates of PSII excitation, To test this hypothesis, the effect of the dark interval between single turnover flashes on the inactivation of water oxidation, charge separation and recombination, and the degradation of D1 protein were determined in spinach thylakoids, PSII inactivation per flash increases as the dark interval between the flashes increases, and a plateau is reached at dark intervals, allowing complete charge recombination of the Q(B)(.-)/S-2,S-3 or Q(A)(.-)/S-2 states (about 200 and 40 s, respectively), At these excitation rates: (i) 0.7% and 0.4% of PSII is inactivated and 0.4% and 0.2% of the D1 protein is degraded per flash, respectively, and (ii) the damage per flash is about 2 orders of magnitude higher than that induced by equal amount of energy delivered by excess continuous light, No PSII damage occurs if flashes are given in anaerobic conditions, These results demonstrate that charge recombination in active PSII is promoted by low rates of excitation and may account for a the high quantum efficiency of the rapid turnover of the DI protein induced by limiting light.