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首页> 外文期刊>Biochemistry >The Orbital Ground State of the Azide Substrate Complex of Human Heme Oxygenase Is an Indicator of Distal H-Bonding: Implications for the Enzyme Mechanism
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The Orbital Ground State of the Azide Substrate Complex of Human Heme Oxygenase Is an Indicator of Distal H-Bonding: Implications for the Enzyme Mechanism

机译：人血红素加氧酶叠氮底物复合物的轨道基态是远端氢键的指标：对酶机制的影响。

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The active site electronic structure of the azide complex of substrate-bound human hemenoxygenase 1 (hHO) has been investigated by 1nH NMR spectroscopy to shed light on the orbital/spinnground state as an indicator of the unique distal pocket environment of the enzyme. Two-dimensionaln1nHnNMR assignments of the substrate and substrate-contact residue signals reveal a pattern of substrate methylncontact shifts that places the lone iron π-spin in the dxz orbital, rather than the dyz orbital found in thencyanide complex. Comparison of iron spin relaxivity, magnetic anisotropy, and magnetic susceptibilitiesnargues for a low-spin, (dxy)n2n(dyz,dxz)n3n, ground state in both azide and cyanide complexes. The switch fromnsingly occupied dyz for the cyanide to dxz for the azide complex of hHO is shown to be consistent with thenorbital hole determined by the azide π-plane in the latter complex, which is ∼90° in-plane rotated fromnthat of the imidazole π-plane. The induction of the altered orbital ground state in the azide relative to thencyanide hHO complex, as well as the mean low-field bias of methyl hyperfine shifts and their paramagneticnrelaxivity relative to those in globins, indicates that azide exerts a stronger ligand field in hHO than in thenglobins, or that the distal H-bonding to azide is weaker in hHO than in globins. The Asp140 f Ala hHOnmutant that abolishes activity retains the unusual WT azide complex spin/orbital ground state. The relevancenof our findings for other HO complexes and the HO mechanism is discussed.
机译：已通过1nH NMR光谱研究了与底物结合的人类血氧合酶1（hHO）的叠氮化物复合物的活性位电子结构，以阐明在轨道/纺纱基态上的光，作为该酶独特的远端囊袋环境的指标。底物和底物接触残基信号的二维n1nHnNMR分配揭示了底物甲基n接触位移的模式，该位移将单独的铁π自旋置于dxz轨道中，而不是在氰化物络合物中发现的dyz轨道。叠氮化物和氰化物配合物的低自旋（dxy）n2n（dyz，dxz）n3n基态的铁自旋弛豫性，磁各向异性和磁化率的比较。已显示从hHO的氰化物占据的dyz到hHO的叠氮化物络合物的dxz的转换与叠氮化物π平面在后者的络合物​​中确定的轨孔相符，该平面从咪唑π的平面旋转约90°飞机。相对于氰化物hHO络合物，叠氮化物中轨道基态的改变，以及甲基高纤位移的平均低场偏度及其相对于球蛋白的顺磁弛豫性，表明叠氮化物在hHO中的配体场强于则说明在HHO中远侧H键与叠氮化物的结合比在球蛋白中弱。消除活性的Asp140 f Ala hHonmutant保留了异常的WT叠氮化物复合物自旋/轨道基态。讨论了我们发现的其他HO配合物和HO机制的相关性。

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  • 来源
    《Biochemistry》 |2009年第14期|p.3127-3137|共11页
  • 作者

    Hiroshi Ogura John P. Evans Dungeng Peng James D. Satterlee Paul R. Ortiz de Montellano;

  • 作者单位

    Department of Chemistry, Uni ersity of California, Da is, California 95616, Department of Chemistry, Washington StateUni ersity, Pullman, Washington 99163, and Department of Pharmaceutical Chemistry, Uni ersity of California,600 16th Street, San Francisco, California 94158-2517;

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