Molecular Biomimetics, Department of Chemistry-Ångström Laboratory, Uppsala University, 751 20 Uppsala, Sweden.
Proc Natl Acad Sci U S A. 2013 Apr 30;110(18):7223-8. doi: 10.1073/pnas.1220645110. Epub 2013 Apr 15.
Photobiological H2 production is an attractive option for renewable solar fuels. Sulfur-deprived cells of Chlamydomonas reinhardtii have been shown to produce hydrogen with the highest efficiency among photobiological systems. We have investigated the photosynthetic reactions during sulfur deprivation and H2 production in the wild-type and state transition mutant 6 (Stm6) mutant of Chlamydomonas reinhardtii. The incubation period (130 h) was dissected into different phases, and changes in the amount and functional status of photosystem II (PSII) were investigated in vivo by electron paramagnetic resonance spectroscopy and variable fluorescence measurements. In the wild type it was found that the amount of PSII is decreased to 25% of the original level; the electron transport from PSII was completely blocked during the anaerobic phase preceding H2 formation. This block was released during the H2 production phase, indicating that the hydrogenase withdraws electrons from the plastoquinone pool. This partly removes the block in PSII electron transport, thereby permitting electron flow from water oxidation to hydrogenase. In the Stm6 mutant, which has higher respiration and H2 evolution than the wild type, PSII was analogously but much less affected. The addition of the PSII inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea revealed that ∼80% of the H2 production was inhibited in both strains. We conclude that (i) at least in the earlier stages, most of the electrons delivered to the hydrogenase originate from water oxidation by PSII, (ii) a faster onset of anaerobiosis preserves PSII from irreversible photoinhibition, and (iii) mutants with enhanced respiratory activity should be considered for better photobiological H2 production.
光生物制氢是可再生太阳能燃料的一个有吸引力的选择。已证明在光生物系统中，缺硫的莱茵衣藻细胞具有最高的产氢效率。我们研究了野生型和状态转换突变体 6（Stm6）突变体的缺硫和产氢过程中的光合作用反应。将 130 小时的孵育期（incubation period）分为不同阶段，并通过电子顺磁共振波谱和可变荧光测量来研究体内光合作用系统 II（PSII）的数量和功能状态的变化。在野生型中，发现 PSII 的数量减少到原始水平的 25％；在形成 H2 之前的厌氧阶段，PSII 的电子传递完全被阻断。在 H2 产生阶段，这种阻断被释放，表明氢化酶从质醌库中提取电子。这部分消除了 PSII 电子传递中的阻断，从而允许电子从水氧化流向氢化酶。在 Stm6 突变体中，其呼吸作用和 H2 释放比野生型更高，PSII 也受到类似但影响较小。加入 PSII 抑制剂 3-(3,4-二氯苯基）-1,1-二甲基脲表明，两种菌株中约有 80％的 H2 产生被抑制。我们得出结论：（i）至少在早期阶段，大部分传递给氢化酶的电子来自 PSII 的水氧化，（ii）更快的厌氧起始时间使 PSII 免于不可逆的光抑制，（iii）具有增强呼吸活性的突变体应被考虑用于更好的光生物制氢。
