Razeghifard M Reza, Chen Min, Hughes Joseph L, Freeman Joel, Krausz Elmars, Wydrzynski Tom
Photobioenergetics, Research School of Biological Sciences, The Australian National University, Canberra, ACT 0200, Australia.
Biochemistry. 2005 Aug 23;44(33):11178-87. doi: 10.1021/bi048314c.
Photosystem II (PSII) electron transfer (ET) in the chlorophyll d-containing cyanobacterium Acaryochloris marina (A. marina) was studied by time-resolved electron paramagnetic resonance (EPR) spectroscopy at room temperature, chlorophyll fluorescence, and low-temperature optical spectroscopy. To maximize the ability to measure PSII ET in the intact cells of this organism, growth conditions were optimized to provide the highest specific O(2) activity and the instrumental parameters for the EPR measurements of tyrosine Z (Y(Z)) reduction were adjusted to give the best signal-to-noise over spectral resolution. Analysis of the Y(Z)(*) reduction kinetics revealed that ET to the oxygen-evolving complex on the donor side of PSII in A. marina is indistinguishable from that in higher plants and other cyanobacteria. Likewise, the charge recombination kinetics between the first plastoquinone acceptor Q(A) and the donor side of PSII monitored by the chlorophyll fluorescence decay on the seconds time scale are not significantly different between A. marina and non-chlorophyll d organisms, while low-temperature optical absorption spectroscopy identified the primary electron acceptor in A. marina as pheophytin a. The results indicate that, if the PSII primary electron donor in A. marina is made up of chlorophyll d instead of chlorophyll a, then there must be very different interactions with the protein environment to account for the ET properties, which are similar to higher plants and other cyanobacteria. Nevertheless, the water oxidation mechanism in A. marina is kinetically unaltered.
通过室温下的时间分辨电子顺磁共振（EPR）光谱、叶绿素荧光和低温光谱学，对含叶绿素d的蓝细菌海栖热袍菌（A. marina）中的光系统II（PSII）电子转移（ET）进行了研究。为了最大限度地提高在该生物体完整细胞中测量PSII ET的能力，优化了生长条件以提供最高的比O(2)活性，并调整了用于酪氨酸Z（Y(Z)）还原的EPR测量的仪器参数，以在光谱分辨率上获得最佳信噪比。对Y(Z)(*)还原动力学的分析表明，海栖热袍菌中PSII供体侧到放氧复合体的电子转移与高等植物和其他蓝细菌中的电子转移没有区别。同样，在秒时间尺度上通过叶绿素荧光衰减监测的第一个质体醌受体Q(A)与PSII供体侧之间的电荷复合动力学在海栖热袍菌和非叶绿素d生物体之间没有显著差异，而低温光吸收光谱确定海栖热袍菌中的初级电子受体为脱镁叶绿素a。结果表明，如果海栖热袍菌中的PSII初级电子供体由叶绿素d而不是叶绿素a组成，那么与蛋白质环境的相互作用必然非常不同，以解释其与高等植物和其他蓝细菌相似的电子转移特性。然而，海栖热袍菌中的水氧化机制在动力学上没有改变。
