Institut de Biologie Physico-Chimique, Unité Mixte de Recherche 7141, Centre National de la Recherche Scientifique-Université Paris 6, 13 Rue Pierre et Marie Curie, 75005 Paris, France.
Nat Commun. 2011;2:301. doi: 10.1038/ncomms1299.
Central in respiration or photosynthesis, the cytochrome bc(1) and b(6)f complexes are regarded as functionally similar quinol oxidoreductases. They both catalyse a redox loop, the Q-cycle, which couples electron and proton transfer. This loop involves a bifurcated electron transfer step considered as being mechanistically mandatory, making the Q-cycle indispensable for growth. Attempts to falsify this paradigm in the case of cytochrome bc(1) have failed. The rapid proteolytic degradation of b(6)f complexes bearing mutations aimed at hindering the Q-cycle has precluded so far the experimental assessment of this model in the photosynthetic chain. Here we combine mutations in Chlamydomonas that inactivate the redox loop but preserve high accumulation levels of b(6)f complexes. The oxidoreductase activity of these crippled complexes is sufficient to sustain photosynthetic growth, which demonstrates that the Q-cycle is dispensable for oxygenic photosynthesis.
细胞色素 bc1（复合体）和 b6f（复合体）在呼吸作用或光合作用中起核心作用，被认为是功能相似的醌氧化还原酶。它们都催化一个氧化还原环，即 Q 循环，它将电子和质子转移偶联起来。这个循环涉及一个分叉的电子转移步骤，被认为在机制上是强制性的，使得 Q 循环对生长是不可或缺的。在细胞色素 bc1（复合体）的情况下，试图推翻这一范式的尝试都失败了。由于旨在阻碍 Q 循环的 b6f（复合体）突变体的快速蛋白水解降解，迄今为止，该模型在光合作用链中的实验评估一直受到阻碍。在这里，我们结合了在衣藻中失活氧化还原环但保留高积累水平的 b6f 复合体的突变。这些受损复合体的氧化还原酶活性足以维持光合作用生长，这表明 Q 循环对于放氧光合作用是可有可无的。
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