Webber A N, Su H, Bingham S E, Käss H, Krabben L, Kuhn M, Jordan R, Schlodder E, Lubitz W
Department of Botany, Arizona State University, Tempe 85287-1601, USA.
Biochemistry. 1996 Oct 1;35(39):12857-63. doi: 10.1021/bi961198w.
Photosystem I is a member of the iron-sulfur center or type I reaction centers. The primary electron donor in photosystem I is a chlorophyll a dimer termed P700. The biophysical properties of P700 are well understood, but the protein environment that gives it such unique properties is unknown. We have characterized site-directed mutants of the photosystem I reaction center protein PsaB and identified an amino acid, His-656, that interacts closely with one of the P700 chlorophylls. Mutation of His-656 to Asn or Ser increases the oxidation midpoint potential of P700/P700+. by 40 mV. The P700/P700+. optical difference spectra show the appearance of a new bleaching band at 667 nm. Electron nuclear double resonance spectroscopy indicates a significant increase in the hyperfine coupling corresponding to methyl protons at position 12 of the spin carrying chlorophyll a of P700+. The implication of these results to current structural models of the photosystem I reaction center is discussed.
光系统I是铁硫中心或I型反应中心的成员之一。光系统I中的初级电子供体是一种被称为P700的叶绿素a二聚体。P700的生物物理特性已得到充分了解，但其赋予P700如此独特性质的蛋白质环境尚不清楚。我们对光系统I反应中心蛋白PsaB的定点突变体进行了表征，并鉴定出一个与P700叶绿素之一紧密相互作用的氨基酸His-656。将His-656突变为Asn或Ser会使P700/P700 +的氧化中点电位增加40 mV。P700/P700 +的光学差光谱显示在667 nm处出现一条新的漂白带。电子核双共振光谱表明，与P700 +自旋携带叶绿素a第12位甲基质子对应的超精细耦合显著增加。本文讨论了这些结果对光系统I反应中心当前结构模型的意义。
