DeRose V J, Yachandra V K, McDermott A E, Britt R D, Sauer K, Klein M P
Department of Chemistry, Lawrence Berkeley Laboratory, University of California, Berkeley 94720.
Biochemistry. 1991 Feb 5;30(5):1335-41. doi: 10.1021/bi00219a025.
The possibility of nitrogen ligation to the Mn in the oxygen-evolving complex from photosystem II was investigated with electron paramagnetic resonance (EPR) and electron spin echo envelope modulation (ESEEM) spectroscopies using 14N- and 15N-labeled preparations. Oxygen-evolving preparations were isolated from a thermophilic cyanobacterium, Synechococcus sp., grown on a medium containing either 14NO3- or 15NO3- as the sole source of nitrogen. the substructure on the "multiline" EPR signal, which arises from Mn in the S2 state of the enzyme, was measured with continuous-wave EPR. No changes were detected in the substructure peak positions upon substitution of 15N for 14N, indicating that this substructure is not due to superhyperfine coupling from nitrogen ligands. To detect potential nitrogen ligands with superhyperfine couplings of lesser magnitude than could be observed with conventional EPR methods, electron spin-echo envelope modulation experiments were also performed on the multiline EPR signal. The Fourier transform of the light-minus-dark time domain ESEEM data shows a peak at 4.8 MHz in 14N samples which is absent upon substitution with 15N. This gives unambiguous evidence for weak hyperfine coupling of nitrogen to the Mn of the oxygen-evolving complex. Possible origins of this nitrogen interaction are discussed.
利用电子顺磁共振（EPR）和电子自旋回波包络调制（ESEEM）光谱，使用14N和15N标记的样品，研究了光系统II放氧复合体中氮与锰结合的可能性。放氧样品从嗜热蓝藻集胞藻属（Synechococcus sp.）中分离得到，该藻在以14NO3-或15NO3-作为唯一氮源的培养基上生长。利用连续波EPR测量了酶的S2状态下由锰产生的“多线”EPR信号的亚结构。用15N取代14N后，未检测到亚结构峰位置的变化，这表明该亚结构不是由氮配体的超超精细耦合引起的。为了检测具有比传统EPR方法所能观察到的更小超超精细耦合的潜在氮配体，还对多线EPR信号进行了电子自旋回波包络调制实验。光减暗时域ESEEM数据的傅里叶变换显示，14N样品在4.8 MHz处有一个峰，用15N取代后该峰消失。这为氮与放氧复合体的锰之间的弱超精细耦合提供了明确的证据。讨论了这种氮相互作用的可能来源。
