ESEEM study of the phyllosemiquinone radical A(1)(center dot-) in N-14- and N-15-labeled photosystem I
ESEEM study of the phyllosemiquinone radical A(1)(center dot-) in N-14- and N-15-labeled photosystem I
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DOI：
10.1021/bi971360a
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发表时间：
1997-09-30
期刊：
影响因子：
2.9
通讯作者：
Rutherford, AW
中科院分区：
文献类型：
--
作者：
Hanley, J;Deligiannakis, Y;Rutherford, AW
用电子自旋回波包络调制(ESEEM)谱研究了光系统I反应中心的叶半醌自由基。对N-14和N-15标记的PSI的ESEEM数据的比较分析和数值模拟表明，存在两个与半喹酮耦合的蛋白质氮核，其中一个N-14偶联的特征是四极耦合常数e(2)qq/4h为0.77 MHz，不对称参数ETA为0.18，以及一个具有几乎纯各向同性超精细耦合的超精细耦合张量，即(A(Xx)，k(Yy)，A(Zz)=(1.3，1.3，1.5 MHz)，第二个氮耦合的特征是四极耦合常数e(2)qq/4h为0.45 MHz，非对称参数eta为0.85，弱超精细耦合张量具有主要的各向异性部分，即(A(Xx)，A(Yy)，A(Zz))=(-0.2，-0.2，1.5 MHz)。根据N-14-ESEEM数据与文献中N-14-NQR和N-14-ESEEM数据的比较，第一个偶联氮被指定为色氨酸残基的吲哚氮，第二个氮的偶合程度要弱得多，因此更难指认。然而，模拟光谱最好地描述了组氨酸的氨基氮，尽管不能排除天冬酰胺或谷氨酰胺的氨基。根据PSI中与半喹酮相近的氨基酸残基讨论了氮超精细偶联的可能来源。
The phyllosemiquinone radical of the photosystem I reaction center has been studied by electron spin echo envelope modulation (ESEEM) spectroscopy, A comparative analysis of ESEEM data of the semiquinone in N-14- and N-15-labeled PSI and numerical simulations demonstrate the existence of two protein nitrogen nuclei coupled to the semiquinone, One of the N-14 couplings is characterized by a quadrupolar coupling constant e(2)qQ/4h of 0.77 MHz, an asymmetry parameter eta of 0.18, and a hyperfine coupling tensor with an almost pure isotropic hyperfine coupling, i.e. (A(xx), k(yy), A(zz)) = (1.3, 1.3, 1.5 MHz), The second nitrogen coupling is characterized by a quadrupolar coupling constant e(2)qQ/4h of 0.45 MHz, an asymmetry parameter eta of 0.85, and a weak hyperfine coupling tensor with a dominant anisotropic part, i.e. (A(xx), A(yy), A(zz)) = (-0.2, -0.2, 1.5 MHz). On the basis of a comparison of the N-14-ESEEM data with N-14-NQR and N-14-ESEEM data from the literature, the first coupled nitrogen is assigned to the indole nitrogen of a tryptophan residue, The coupling of the second nitrogen is much weaker and therefore more difficult to assign. However, the simulated spectrum best describes an amino nitrogen of a histidine, although the amide group of an asparagine or glutamine cannot be ruled out. The possible origins of the nitrogen hyperfine coupling are discussed in terms of the amino acid residues thought to be close to the semiquinone in PSI.