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首页> 外文学位 >Proton transfer reactions in photosynthetic water oxidation: Second sphere ligands of the manganese cluster modulate the water oxidation mechanism of photosystem ii.
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Proton transfer reactions in photosynthetic water oxidation: Second sphere ligands of the manganese cluster modulate the water oxidation mechanism of photosystem ii.

机译：光合水氧化中的质子转移反应：锰团簇的第二球配体调节光系统ii的水氧化机理。

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摘要

In the D1-D61N mutant, it was possible to resolve a clear lag phase prior to the appearance of O2, indicating formation of an intermediate before onset of O2 formation. The lag phase and the photochemical miss factor were more sensitive to isotope substitution in the mutant indicating that proton efflux in the mutant proceeds via an alternative pathway. The results are discussed in comparison with earlier results obtained from the substitution of CP43-Arg357 with lysine and in regards to hypotheses concerning the nature of the final steps in photosynthetic water oxidation. These considerations lead to the conclusion that proton expulsion during the initial phase of the S3-S0 transition starts with the deprotonation of primary catalytic base, probably CP43-Arg357, followed by efficient proton egress involving the carboxyl group of D1-D61 in a process that constitutes the lag phase immediately prior to O2 formation chemistry. The asparagine, phenylalanine and threonine substitutions to D1-V185 were able to accumulate significant levels of charge separating PSII. Of the three substitutions the phenylalanine substitution was the most severe with a complete inability to evolve oxygen, despite being able to accumulate Photosystem II and to undergo stable charge separations. The threonine substitution had no apparent effect on oxygen evolution other than a 40% reduction in the steady state rate of O2 production compared to type Synechocystis, which can be attributed to that mutants reduced ability to accumulate PSII. The asparagine substitution produced the most complex phenotype. While still able to evolve oxygen, it does so less efficiently than wild type PSII, with a miss factor 4% higher than wild type Synechocystis. The substitution on D1-Val185 with asparagine also decreased the t1/2 of O2 release from thylakoid membranes from 1.2 ms to 10.0 ms and decreased the t1/2 lag phase prior to the onset of O2 release to 2.8 ms. The combination of a long lag period and a decreased rate of O2 release can also be observed in the D1-D61N mutant strains of Synechocystis and in PSII centers in which chloride has been replaced by iodide.
机译：在D1-D61N突变体中，有可能在O2出现之前解决一个清晰的滞后阶段，这表明在O2形成开始之前就形成了中间体。滞后相和光化学缺失因子对突变体中的同位素取代更敏感，表明突变体中的质子外排通过替代途径进行。与将CP43-Arg357替换为赖氨酸得到的早期结果进行了比较，并讨论了有关光合水氧化最终步骤的性质的假设。这些考虑得出这样的结论：在S3-S0过渡的初始阶段，质子的排出开始于主要的催化碱（可能是CP43-Arg357）的去质子化，然后是有效的质子逸出，其中涉及D1-D61的羧基。刚好在O2形成化学之前就构成了滞后阶段。 D1-V185的天冬酰胺，苯丙氨酸和苏氨酸取代能够积累大量的电荷，从而分离PSII。在这三个取代中，苯丙氨酸取代是最严重的，尽管能够积累光系统II并进行稳定的电荷分离，但完全不能释放出氧气。苏氨酸取代对氧气的释放没有明显影响，只是与Synechocystis类型相比，O2产生的稳态速率降低了40％，这可以归因于突变体降低了PSII的积累能力。天冬酰胺取代产生最复杂的表型。尽管仍然能够释放氧气，但它的效率要比野生型PSII低，而漏失因子却比野生型集囊藻高4％。在D1-Val185上用天冬酰胺取代还可以将类囊体膜上的O2释放的t1 / 2从1.2 ms降低到10.0 ms，并在开始释放O2之前将t1 / 2滞后阶段降低到2.8 ms。还可以在集胞藻的D1-D61N突变株中以及在其中氯化物已被碘化物替代的PSII中心中观察到较长的滞后期和降低的O2释放速率。

著录项

  • 作者

    Dilbeck, Preston Lee.;

  • 作者单位

    Oklahoma State University.;

  • 授予单位 Oklahoma State University.;
  • 学科 Biology Molecular.;Chemistry Biochemistry.;Biophysics General.
  • 学位 Ph.D.
  • 年度 2012
  • 页码 114 p.
  • 总页数 114
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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