Genes encoding a-type flavoproteins are essential for photoreduction of O2 in cyanobacteria
Genes encoding a-type flavoproteins are essential for photoreduction of O2 in cyanobacteria
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DOI：
10.1016/s0960-9822(03)00046-0
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发表时间：
2003-02-04
期刊：
影响因子：
9.2
通讯作者：
Kaplan, A
中科院分区：
文献类型：
--
作者：
Helman, Y;Tchernov, D;Kaplan, A
通过光合电子转移的O-2光还原反应，即Mehler反应[1]，在所有的产氧光合生物中都观察到[2-4]，但是介导该反应的电子传递链仍然没有确定。我们提供了参与A型黄素蛋白的第一个证据;在体外将O2直接还原为水。集胞藻菌株PCC 6803缺失flv 1和flv 3，编码A型黄素蛋白，不能表现出O-2光还原，但进行正常的光合作用和呼吸。我们表明，光增强O-2吸收不是由于呼吸或光呼吸。黑暗驯化后，P-700的光氧化在突变体Deltaflv 1和Deltaflv 3中被严重抑制，但在光活化CO2固定后恢复，这给P-700提供了额外的电子受体。抑制CO2固定阻止恢复，但几乎没有影响P-700氧化的野生型，其中的Mehler反应提供了一个替代途径的电子。我们的结论是O-2光还原的电子源是PSI和高度保守的A型黄素蛋白Flv 1和Flv 3是必不可少的，在体内的这个过程。我们建议，在蓝藻，相反的真核生物，梅勒反应不产生活性氧物种，并可能在进化上相关的厌氧细菌O-2的反应。
O-2 photoreduction by photosynthetic electron transfer, the Mehler reaction [1], was observed in all groups of oxygenic photosynthetic organisms [2-4], but the electron transport chain mediating this reaction remains unidentified. We provide the first evidence for the involvement of A-type flavoproteins; that reduce 02 directly to water in vitro. Synechocystis sp. strain PCC 6803 mutants defective in flv1 and flv3, encoding A-type flavoproteins, failed to exhibit O-2 photoreduction but performed normal photosynthesis and respiratiom We show that the light-enhanced O-2 uptake was not due to respiration or photorespiration. After dark acclimation, photooxidation of P-700 was severely depressed in mutants Deltaflv1 and Deltaflv3 but recovered after light activation of CO2 fixation, which gives P-700 an additional electron acceptor. Inhibition of CO2 fixation prevented recovery but scarcely affected P-700 oxidation in the wild-type, where the Mehler reaction provides an alternative route for electrons. We conclude that the source of electrons for O-2 photoreduction is PSI and that the highly conserved A-type flavoproteins Flv1 and Flv3 are essential for this process in vivo. We propose that in cyanobacteria, contrary to eukaryotes, the Mehler reaction produces no reactive oxygen species and may be evolutionarily related to the response of anaerobic bacteria to O-2.