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首页> 外文期刊>Biochemistry >ESEEM STUDY OF THE PLASTOQUINONE ANION RADICAL (Q(A)(CENTER-DOT-)) IN N-14- AND N-15-LABELED PHOTOSYSTEM II TREATED WITH CN
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ESEEM STUDY OF THE PLASTOQUINONE ANION RADICAL (Q(A)(CENTER-DOT-)) IN N-14- AND N-15-LABELED PHOTOSYSTEM II TREATED WITH CN

机译：用CN处理N-14和N-15标记的光系统II中塑料醌阴离子自由基（Q（A）（CENTER-DOT-））的ESEEM研究

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摘要

The nonheme iron of the photosystem II reaction center was converted to its low-spin state (S = 0) by treatment with CN-. This allowed the study of the plastoquinone, Q(A)(-) anion radical by electron spin-echo envelope modulation (ESEEM) spectroscopy. A comparative analysis of the ESEEM data of Q(A)(-) in N-14- and N-15-labeled PSII demonstrates the existence of a protein nitrogen nucleus coupled to the Q(A)(-). The N-14 coupling is characterized by a quadrupolar coupling constant e(2)qQ/4h = 0.82 MHz, an asymmetry parameter eta = 0.45, and hyperfine coupling constant A similar to 2.1 MHz. The N-15 hyperfine coupling is characterized by T = 0.41 MHz and alpha(iso) similar to 3.3 MHz. The possible origins of the nitrogen hyperfine coupling are discussed in terms of the amino acids thought to be close to the Q(A)(-) in PSII. Based on a comparison of the N-14 ESEEM with N-14-NQR and N-14-ESEEM data from the literature, the most likely candidate is the amide nitrogen of the peptide backbone of Ala261 of the polypeptide D2, although the indole nitrogen of Trp254 and the imino nitrogen of His215 of D2 also remain candidates.
机译：通过用CN-处理，光系统II反应中心的非血红素铁转化为低自旋状态（S = 0）。这使得可以通过电子自旋回波包络调制（ESEEM）光谱研究质体醌Q（A）（-）阴离子自由基。对N-14-和N-15标记的PSII中Q（A）（-）的ESEEM数据进行的比较分析表明，存在与Q（A）（-）偶联的蛋白质氮核。 N-14耦合的特征是四极耦合常数e（2）qQ / 4h = 0.82 MHz，不对称参数eta = 0.45，超精细耦合常数A类似于2.1 MHz。 N-15超精细耦合的特征在于T = 0.41 MHz和类似于3.3 MHz的alpha（iso）。氮超精细偶联的可能起源是根据认为与PSII中的Q（A）（-）接近的氨基酸进行讨论的。根据文献中N-14 ESEEM与N-14-NQR和N-14-ESEEM数据的比较，最可能的候选化合物是多肽D2的Ala261肽骨架的酰胺氮，尽管吲哚氮Trp254的残基和D2的His215的亚氨基氮也保留。

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