Melkozernov Alexander N, Barber James, Blankenship Robert E
Department of Chemistry and Biochemistry and Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe, Arizona 85287-1604, USA.
Biochemistry. 2006 Jan 17;45(2):331-45. doi: 10.1021/bi051932o.
In photosynthetic membranes of cyanobacteria, algae, and higher plants, photosystem I (PSI) mediates light-driven transmembrane electron transfer from plastocyanin or cytochrome c6 to the ferredoxin-NADP complex. The oxidoreductase function of PSI is sensitized by a reversible photooxidation of primary electron donor P700, which launches a multistep electron transfer via a series of redox cofactors of the reaction center (RC). The excitation energy for the functioning of the primary electron donor in the RC is delivered via the chlorophyll core antenna in the complex with peripheral light-harvesting antennas. Supermolecular complexes of the PSI acquire remarkably different structural forms of the peripheral light-harvesting antenna complexes, including distinct pigment types and organizational principles. The PSI core antenna, being the main functional unit of the supercomplexes, provides an increased functional connectivity in the chlorophyll antenna network due to dense pigment packing resulting in a fast spread of the excitation among the neighbors. Functional connectivity within the network as well as the spectral overlap of antenna pigments allows equilibration of the excitation energy in the depth of the whole membrane within picoseconds and loss-free delivery of the excitation to primary donor P700 within 20-40 ps. Low-light-adapted cyanobacteria under iron-deficiency conditions extend this capacity via assembly of efficiently energy coupled rings of CP43-like complexes around the PSI trimers. In green algae and higher plants, less efficient energy coupling in the eukaryotic PSI-LHCI supercomplexes is probably a result of the structural adaptation of the Chl a/b binding LHCI peripheral antenna that not only extends the absorption cross section of the PSI core but participates in regulation of excitation flows between the two photosystems as well as in photoprotection.
在蓝细菌、藻类和高等植物的光合膜中，光系统I（PSI）介导从质体蓝素或细胞色素c6到铁氧化还原蛋白 - NADP复合物的光驱动跨膜电子转移。PSI的氧化还原酶功能通过初级电子供体P700的可逆光氧化而被激活，这会引发通过反应中心（RC）的一系列氧化还原辅因子进行的多步电子转移。RC中初级电子供体发挥功能所需的激发能是通过与外周捕光天线结合的叶绿素核心天线传递的。PSI的超分子复合物具有显著不同结构形式的外周捕光天线复合物，包括不同的色素类型和组织原则。PSI核心天线作为超复合物的主要功能单元，由于色素紧密堆积，使得叶绿素天线网络中的功能连接性增强，从而导致激发能在相邻色素之间快速传播。网络内的功能连接性以及天线色素的光谱重叠使得激发能在皮秒内就能在整个膜的深度达到平衡，并在20 - 40皮秒内将激发能无损地传递给初级供体P700。缺铁条件下适应弱光的蓝细菌通过在PSI三聚体周围组装高效能量耦合的CP43样复合物环来扩展这种能力。在绿藻和高等植物中，真核PSI - LHCI超复合物中效率较低的能量耦合可能是由于Chl a/b结合的LHCI外周天线的结构适应导致的，这种天线不仅扩大了PSI核心的吸收截面，还参与调节两个光系统之间的激发流以及光保护过程。
