一氧化二氮还原酶中混合价态铜位点的多量子电子顺磁共振
Multiquantum EPR of the mixed valence copper site in nitrous oxide reductase.
作者信息
Mchaourab H S, Pfenninger S, Antholine W E, Felix C C, Hyde J S, Kroneck P M
机构信息
National Biomedical ESR Center, Biophysics Research Institute, Medical College of Wisconsin, Milwaukee 53226.
出版信息
Biophys J. 1993 May;64(5):1576-9. doi: 10.1016/S0006-3495(93)81527-3.
This work demonstrates the use of multiquantum EPR to study the magnetic properties of copper complexes and copper proteins. Pure absorption spectra are obtained because of the absence of field modulation. The signal intensity of 3-quantum spectra is proportional to the spin lattice relaxation time T1, while its linewidth in a frequency difference sweep is T1(-1). A change in lineshape for the EPR detectable mixed value [Cu(1.5) . . . Cu(1.5)] site in nitrous oxide reductase is attributed to suppression of the forbidden transitions. The data confirm the unusually fast relaxation time for this site, which requires temperatures of less than 100 K to resolve hyperfine structure. The T1's for the mixed valence [Cu(1.5) . . . Cu(1.5)] site in nitrous oxide reductase are very similar to T1's for the Cua site in cytochrome c oxidase. The similar relaxation properties, together with previous multifrequency EPR results, support the hypothesis that the EPR detectable sites in cytochrome c oxidase and nitrous oxide reductase are mixed valence [Cu(1.5) . . . Cu(1.5)] configurations.
这项工作展示了利用多量子电子顺磁共振（EPR）来研究铜配合物和铜蛋白的磁性。由于没有场调制，所以获得了纯吸收光谱。三量子光谱的信号强度与自旋晶格弛豫时间T1成正比，而在频差扫描中其线宽为T1的倒数（T1⁻¹）。一氧化二氮还原酶中EPR可检测的混合价态[Cu(1.5)……Cu(1.5)]位点的线形变化归因于禁戒跃迁的抑制。数据证实了该位点异常快的弛豫时间，这需要低于100 K的温度才能分辨超精细结构。一氧化二氮还原酶中混合价态[Cu(1.5)……Cu(1.5)]位点的T1值与细胞色素c氧化酶中Cua位点的T1值非常相似。相似的弛豫特性，连同之前的多频EPR结果，支持了细胞色素c氧化酶和一氧化二氮还原酶中EPR可检测位点是混合价态[Cu(1.5)……Cu(1.5)]构型的假说。
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