Canne C, Ebelshäuser M, Gay E, Shergill J K, Cammack R, Kappl R, Hüttermann J
Fachrichtung Biophysik und Physikalische Grundlagen der Medizin, Universität des Saarlandes, Homburg/Saar, Germany.
J Biol Inorg Chem. 2000 Aug;5(4):514-26. doi: 10.1007/pl00021451.
The 1H electron nuclear double resonance (ENDOR) spectra in frozen solutions of the reduced [2Fe-2S] cluster in ferredoxin from Arthrospira (Spirulina) platensis have been measured at low temperatures (5-20 K) and simulated using orientational selection methods. The analysis confirmed the existence of a single paramagnetic species with iron valence states II and III connected uniquely to the cluster irons. The experimental ENDOR spectra were fitted to a model including the spin distribution on the centre, the orientation of the g-matrix, and the isotropic and anisotropic hyperfine couplings of the nearest protons in the crystallographically determined structure. In order to partially simulate ENDOR line shapes, a statistical distribution of the corresponding torsion angles between the Fe(III) centre and one of the beta-CH2 protons was introduced. From the analysis, four of the larger hyperfine couplings found were assigned to the cysteine beta-protons near the Fe(III) ion of the cluster, with isotropic hyperfine couplings ranging from 1.6 to 4.1 MHz. The spin distribution on the two iron ions was estimated to be +1.85 for the Fe(III) ion and -0.9 for the Fe(II) ion. The Fe(III) ion was identified as being coordinated to the cysteine ligands Cys49 and Cys79, confirming previous NMR results. The direction of the g-tensor with respect to the cluster was deduced. The g1-g2 plane is parallel to the planes through each iron and its adjacent cysteine sulfurs; the g2-g3 plane is nearly perpendicular to the latter planes and deviates by 25 degrees from the FeSSFe plane. The g1 direction is dominated by the bonding geometry of Fe(II) and does not align with the Fe(II)-Fe(III) vector.
已在低温（5 - 20K）下测量了钝顶螺旋藻铁氧化还原蛋白中还原型[2Fe - 2S]簇冷冻溶液的1H电子核双共振（ENDOR）光谱，并使用取向选择方法进行了模拟。分析证实存在一种单一的顺磁物种，其铁价态为II和III，唯一地与簇铁相连。将实验性ENDOR光谱拟合到一个模型，该模型包括中心的自旋分布、g矩阵的取向以及晶体学确定结构中最近质子的各向同性和各向异性超精细耦合。为了部分模拟ENDOR线形，引入了Fe(III)中心与一个β - CH2质子之间相应扭转角的统计分布。通过分析，发现的四个较大超精细耦合被指定给簇的Fe(III)离子附近的半胱氨酸β - 质子，各向同性超精细耦合范围为1.6至4.1 MHz。估计两个铁离子上的自旋分布为：Fe(III)离子为 + 1.85，Fe(II)离子为 - 0.9。已确定Fe(III)离子与半胱氨酸配体Cys49和Cys79配位，证实了先前的核磁共振结果。推导了g张量相对于簇的方向。g1 - g2平面平行于通过每个铁及其相邻半胱氨酸硫的平面；g2 - g3平面几乎垂直于后述平面，且与FeSSFe平面偏离25度。g1方向由Fe(II)的键合几何结构主导，且不与Fe(II) - Fe(III)向量对齐。
