Addison A W, Stephanos J J
Biochemistry. 1986 Jul 15;25(14):4104-13. doi: 10.1021/bi00362a018.
Nitrosyl complexes of the iron(III) forms of myoglobin, human hemoglobin, Glycera dibranchiata hemoglobins (Hbm and Hbh), and model iron(II) and iron(III) synthetic porphyrins including octaethylporphyrin (OEP) have been prepared. The iron(III) heme proteins are electron spin (paramagnetic) resonance (ESR) silent, while hexacoordinate solution structures are indicated for [Fe(OEP)(NO)2]ClO4 and for Hbm(II)NO, which has an ESR spectrum similar to that of Mb(II)NO and the hexacoordinate iron(II) model complex Fe(OEP)NO(BzIm). The splitting of the alpha- and beta-bands in the optical spectrum of Mb(III)NO and Hbh(III)NO contrasts markedly with the sharp, single bands observed in that of Hbm-(III)NO. The nondegeneracy of the dxz and dyz orbitals in Mb(III)NO and Hbh(III)NO is attributed to the influence of the distal histidine. Circular dichroism spectra were obtained for Hbm(III)NO, Hbm(II)NO, Hbh(III)NO, Hbh(II)NO, Mb(II)NO, and Mb(III)NO. The vicinal chiral center contribution that governs the heme protein CD leads to low Kuhn anisotropies, which have been used to assign certain electronic transitions. The Hb(III)NO spectrum is not stable but transforms into that of Hb(II)NO. This autoredox process follows kinetics that are first order in FeIIINO. The relative rates of autoreduction (25 degrees C, 1 atm NO) are Mb(III)NO less than Hbm(III)NO less than Hb alpha(III)NO less than HbA(III)NO. At high NO partial pressure or after "recycling" of HbA, the rates of reduction decrease. The first step in the reaction of NO with the ferric heme is the reversible formation of the formally iron(III) adduct. This reacts with another molecule of NO, generating the final heme(II)-NO via nitrosylation of NO itself or of an endogenous nucleophile. Kinetic and spectroscopic evidence shows involvement of trans-heme-(NO)2 in the reaction. The activation parameters delta H and delta S were determined. The overall reaction is photoenhanced.
已制备了肌红蛋白、人血红蛋白、双鳃耳乌贼血红蛋白（Hbm和Hbh）的铁（III）形式的亚硝酰配合物，以及包括八乙基卟啉（OEP）在内的模型铁（II）和铁（III）合成卟啉。铁（III）血红素蛋白在电子自旋（顺磁）共振（ESR）中无信号，而[Fe（OEP）（NO）2]ClO4和Hbm（II）NO显示出六配位溶液结构，其ESR光谱与Mb（II）NO和六配位铁（II）模型配合物Fe（OEP）NO（BzIm）的相似。Mb（III）NO和Hbh（III）NO的光谱中α-和β-带的分裂与Hbm-（III）NO中观察到的尖锐单带形成明显对比。Mb（III）NO和Hbh（III）NO中dxz和dyz轨道的非简并性归因于远端组氨酸的影响。获得了Hbm（III）NO、Hbm（II）NO、Hbh（III）NO、Hbh（II）NO、Mb（II）NO和Mb（III）NO的圆二色光谱。控制血红素蛋白CD的邻位手性中心贡献导致低的库恩各向异性，已用于确定某些电子跃迁。Hb（III）NO光谱不稳定，会转变为Hb（II）NO的光谱。这种自动氧化还原过程遵循FeIIINO一级动力学。自动还原的相对速率（25℃，1个大气压NO）为Mb（III）NO＜Hbm（III）NO＜Hbα（III）NO＜HbA（III）NO。在高NO分压或HbA“循环”后，还原速率降低。NO与铁（III）血红素反应的第一步是正式的铁（III）加合物的可逆形成。它与另一个NO分子反应，通过NO自身或内源性亲核试剂的亚硝基化生成最终的血红素（II）-NO。动力学和光谱证据表明反应中涉及反式血红素-（NO）2。测定了活化参数ΔH和ΔS。整个反应是光增强的。
