Chen G X, Kazimir J, Cheniae G M
Plant Physiology, Biochemistry, and Molecular Biology Program, University of Kentucky, Lexington 40546-0091.
Biochemistry. 1992 Nov 17;31(45):11072-83. doi: 10.1021/bi00160a017.
The effects of photosystem II (PSII) exogenous electron donors and acceptors on the kinetics of weak light photoinhibition of NH2OH/EDTA-extracted spinach PSII membranes were examined. Under aerobic conditions, Mn2+ (approximately 1 Mn/reaction center; Km approximately 400 nM) inhibited photoinactivation and approximately 1 Mn/reaction center plus 100 microM NH2NH2 gave almost complete protection. In the absence of electron donors, strict anaerobiosis greatly inhibited photoinactivation even in the presence of an electron acceptor. Under aerobic conditions, the addition of electron acceptors (FeCN, DCIP), oxyradical scavengers, or superoxide dismutase strongly suppressed rates of photodamages. Increase in the concentrations of superoxide above those produced by illuminated NH2OH/EDTA-photosystem II membranes increased the rates of damage in the light but gave no damage in the dark. Scavengers of hydroxyl radicals and singlet oxygen did not suppress the rates of aerobic photoinhibition. These findings, along with others, lead us to conclude that photodamage of the secondary donors of the PSII reaction center occurs by two mechanisms: (1) a rapid superoxide and tyrosine YZ+ dependent process and (2) a slower process in which P680+/Chl+ catalyze the damages.
研究了光系统II（PSII）外源电子供体和受体对NH2OH/EDTA提取的菠菜PSII膜弱光光抑制动力学的影响。在有氧条件下，Mn2+（约1个Mn/反应中心；Km约为400 nM）抑制光失活，约1个Mn/反应中心加100μM肼几乎提供完全保护。在没有电子供体的情况下，严格的厌氧条件即使在有电子受体存在时也会极大地抑制光失活。在有氧条件下，添加电子受体（铁氰化物、2,6-二氯靛酚）、氧自由基清除剂或超氧化物歧化酶会强烈抑制光损伤速率。超氧化物浓度高于光照的NH2OH/EDTA-光系统II膜产生的浓度时，会增加光照下的损伤速率，但在黑暗中不会造成损伤。羟基自由基和单线态氧的清除剂不会抑制有氧光抑制速率。这些发现以及其他发现使我们得出结论，PSII反应中心二级供体的光损伤通过两种机制发生：（1）快速的超氧化物和酪氨酸YZ+依赖性过程，以及（2）较慢的过程，其中P680+/Chl+催化损伤。
