Solution NMR characterization of the electronic structure and magnetic properties of high-spin ferrous heme in deoxy myoglobin from Aplysia limacina.
Solution NMR characterization of the electronic structure and magnetic properties of high-spin ferrous heme in deoxy myoglobin from Aplysia limacina.
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海兔脱氧肌红蛋白中高自旋亚铁血红素的电子结构和磁性的溶液核磁共振表征。
DOI：
10.1021/ja035256u
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发表时间：
2003
期刊：
影响因子：
--
通讯作者：
LaMar,GerdN
中科院分区：
文献类型：
--
作者：
Ma,Dejian;Musto,Raffaella;Smith,KevinM;LaMar,GerdN
本文用~1H NMR研究了海兔（Aaprisialimacina）高自旋亚铁脱氧肌红蛋白辅基的磁性和电子结构。分配了足够数量的偶极位移残基信号，以便能够可靠地确定顺磁磁化率张量χ的方向和各向异性。由此产生的偶极位移的定量描述允许确定的血红素的接触位移。发现χ是轴向的，Δ χ ax = − 2.07 × 10 - 8m3/mol，长轴几乎倾斜（约76 °）进入血红素平面，并且与轴向HisF8咪唑平面的取向大致一致，该平面与β-，δ-内消旋轴大致重合。血红素的因子化接触位移与正π自旋密度转移到最高填充π分子轨道3e π的两个分量之一，以及负π自旋密度通过自旋-自旋相关转移到3e π分子轨道的正交激发态分量是一致的。激发态的热布居导致血红素取代基主要经历负π-自旋密度强烈偏离居里定律。高自旋铁（II）血红素蛋白中负自旋密度通过自旋配对d π轨道向激发态3e π的转移比低自旋铁（III）血红素蛋白大得多，这归因于前者铁上的四个未配对自旋比后者铁上的单个未配对自旋产生更强的相关性。
Solution1H NMR has been used to elucidate the magnetic properties and electronic structure of the prosthetic group in high-spin, ferrous deoxy myoglobin from the sea hareAplysialimacina. A sufficient number of dipolar shifted residue signals were assigned to allow the robust determination of the orientation and anisotropy of the paramagnetic susceptibility tensor, χ. The resulting quantitative description of dipolar shifts allows a determination of the contact shifts for the heme. χ was found to be axial, with Δχax= −2.07 × 10-8m3/mol, with the major axis tilted (∼76°) almost into the heme plane and in the general direction of the orientation of the axial HisF8 imidazole plane which coincides approximately with the β-,δ-meso axis. The factored contact shifts for the heme are shown to be consistent with the transfer ofpositiveπ spin density into one of the two components of the highest filled π molecular orbital, 3eπ, and the transfer ofnegativeπ-spin density, via spin−spin correlation, into the orthogonal excited-state component of the 3eπmolecular orbital. The thermal population of the excited state leads to strong deviation from the Curie law for the heme substituents experiencing primarily the negative π-spin density. The much larger transfer of negative spin density via the spin-paired dπ orbital into the excited state 3eπin high-spin iron(II) than in low-spin iron(III) hemoproteins is attributed to the much stronger correlation exerted by the four unpaired spin on the iron in the former, as compared to the single unpaired spins on iron in the latter.