Location of the iron-sulfur clusters FA and FB in photosystem I: an electron paramagnetic resonance study of spin relaxation enhancement of P700+.
Location of the iron-sulfur clusters FA and FB in photosystem I: an electron paramagnetic resonance study of spin relaxation enhancement of P700+.
复制标题
铁硫簇 FA 和 FB 在光系统 I 中的位置：P700 自旋弛豫增强的电子顺磁共振研究。
DOI：
10.1021/bi9910777
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发表时间：
1999
期刊：
影响因子：
2.9
通讯作者：
Brudvig,GW
中科院分区：
文献类型：
--
作者：
Lakshmi,KV;Jung,YS;Golbeck,JH;Brudvig,GW
光系统I（PS I）通过光化学活性的叶绿素二聚体（P700）、单体叶绿素电子受体（A0）、叶绿醌（A1）和三个[4 Fe-4 S]簇（FX/A/B）介导电子从质体蓝蛋白转移到铁氧还蛋白。铁硫簇、FX和铁氧还蛋白之间的电子转移事件顺序目前尚不清楚。由于铁硫簇FA和FB结合的PsaC蛋白存在2重对称性，这些辅因子相对于PS I中C2对称轴的空间排列也不确定。明确确定蛋白质内铁硫簇FA和FB的空间排列对于解开PS I中完整的电子传递链是必要的。在本研究中，我们从电荷分离的自旋对（P700+-）产生EPR信号， ）在PS I中，并通过渐进式微波功率饱和测量来表征它们，以确定铁硫簇FX/A/B相对于P700的排列。P700+的半饱和微波功率（P1/2）在未处理的PS I中当FA和FB都被还原时比在汞处理的PS I中仅FA被还原时大。实验的P1/2值与通过使用P700-FA/B晶体学距离并假设FA或FB更接近P700+计算的值进行比较。在比较P700+[4Fe-4S]-电荷分离对中P700+自旋弛豫增强效应的实验值和理论值的基础上，我们发现铁硫团簇FA比FB团簇更接近P700。
Photosystem I (PS I) mediates electron-transfer from plastocyanin to ferredoxin via a photochemically active chlorophyll dimer (P700), a monomeric chlorophyll electron acceptor (A0), a phylloquinone (A1), and three [4Fe-4S] clusters (FX/A/B). The sequence of electron-transfer events between the iron−sulfur cluster, FX, and ferredoxin is presently unclear. Owing to the presence of a 2-fold symmetry in the PsaC protein to which the iron−sulfur clusters FAand FBare bound, the spatial arrangement of these cofactors with respect to the C2-axis of symmetry in PS I is uncertain as well. An unequivocal determination of the spatial arrangement of the iron−sulfur clusters FAand FBwithin the protein is necessary to unravel the complete electron-transport chain in PS I. In the present study, we generate EPR signals from charge-separated spin pairs (P700+- ) in PS I and characterize them by progressive microwave power saturation measurements to determine the arrangement of the iron−sulfur clusters FX/A/Brelative to P700. The microwave power at half saturation (P1/2) of P700+is greater when both FAand FBare reduced in untreated PS I than when only FAis reduced in mercury-treated PS I. The experimentalP1/2values are compared to values calculated by using P700-FA/Bcrystallographic distances and assuming that either FAor FBis closer to P700+. On the basis of this comparison of experimental and theoretical values of spin relaxation enhancement effects on P700+in P700+[4Fe-4S]-charge-separated pairs, we find that iron−sulfur cluster FAis in closer proximity to P700than the FBcluster.