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The Magnetic Properties of Myoglobin as Studied by NMR Spectroscopy

机译：肌红蛋白的磁性通过NMR光谱研究

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Deoxymyoglobin has been investigated by NMR spectrsocopy to determine the magnetic anisotropy through pseudocontant shifts and the total magnetic susceptibility through Evans measurements. The magnetic anisotropy values were found to be DELTAchi_ax = -2.03 (+-) 0.08 X 10~(-32) m~3 and DELTAchi_rh = -1.02 (+-) 0.09 X 10~(-32) m~3. The negative value of the axial susceptibility anisotropy originates from the z tensor axis lying in the heme plane, unlike all other heme sytems investigated so far. This magnetic axis is almost exactly orthogonal to the axial histidine plane. The other two axes lie essentially in the histidine plane, the closest to the heme normal being titled by about 36 deg from it, towards pyrrole A on the side of the proximal hisitidine. From the comparison with cytochorme c' it clearly appears that the position of the one axis lying in the heme plane is related to the axial histidine orientation. Irrespective of the directions, the magnetic anisotropy is smaller than that of the analogous reduced chtochrome c' and of the order of that of low-spin iron(III). The magnetic anistropy of the system permits the measurement of residual dipolar couplings, which, together with pseudocontact shifts, prove that the solution structure is very similar to that in the crystalline state. Magnetic measurements, at variance ith previous data, demonstrate that there is an orbital contribution to the magnetic moment, mu_eff = 5.5 mu_B. Finally, from the magnetic anistropy data, the hyperfine shifts of iron ligands could be separated in pseudocontact and contact components, and hints are provided to understand the spin-delocalisation mechanism in S = 2 systems by keeping in mind the delocalisation patterns in low-spin S = 1/2 and high-spin S = 5/2 iron(III) systems.
机译：已通过NMR光谱对脱氧肌红蛋白进行了研究，以通过伪常数位移确定磁各向异性，并通过Evans测量确定总磁化率。磁各向异性值被发现为DELTAchi_ax = -2.03（+/-）0.08 X 10〜（-32）m〜3和DELTAchi_rh = -1.02（+/-）0.09 X 10〜（-32）m〜3。与迄今为止研究的所有其他血红素系统不同，轴向磁化率各向异性的负值源自位于血红素平面的z张量轴。该磁轴几乎完全与轴向组氨酸平面正交。另外两个轴基本上位于组氨酸平面内，最靠近血红素法线的方向是从其指向近组氨酸侧面的吡咯A约36度。从与细胞色素c'的比较可以清楚地看出，位于血红素平面中的一个轴的位置与轴向组氨酸的取向有关。不论方向如何，其磁各向异性都小于类似的还原型五氧化铬c'的磁各向异性，并且约为低旋转铁（III）的磁各向异性。该系统的磁各向异性可以测量残留的偶极耦合，连同伪接触位移一起证明了溶液的结构与晶体状态非常相似。磁测量值与以前的数据不同，表明对磁矩的轨道贡献为mu_eff = 5.5 mu_B。最后，从磁人类学数据中，可以将铁配体的超精细位移分离成伪接触和接触成分，并且通过记住低旋转中的离域模式，提供了一些提示以了解S = 2系统中的自旋离域机制。 S = 1/2和高转速S = 5/2铁（III）系统。

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