RESONANCE RAMAN AND EPR SPECTROSCOPIC STUDIES ON HEME HEME OXYGENASE COMPLEXES
RESONANCE RAMAN AND EPR SPECTROSCOPIC STUDIES ON HEME HEME OXYGENASE COMPLEXES
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DOI：
10.1021/bi00214a012
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发表时间：
1993-12-28
期刊：
影响因子：
2.9
通讯作者：
LOEHR, TM
中科院分区：
文献类型：
--
作者：
SUN, J;WILKS, A;LOEHR, TM
利用光学吸收光谱、共振拉曼光谱和EPR光谱研究了亚铁血红素和铁血红素、锰(II)-和锰(III)-取代血红素与血红素加氧酶的结合。结果与六坐标血红素片段连接到必需组氨酸配体和水分子的存在是一致的。后者电离时的pK(a)几乎等于8.0，得到高自旋和低自旋六坐标羟基加合物的混合物。过量氰化物的加入将血红素转化为六配位低自旋物质。铁血红素-血红素加氧酶复合物和锰（II）原卟啉-血红素加氧酶复合物的共振拉曼光谱分别显示在216和212 cm-1处，属于金属-组氨酸拉伸模式。氧化血红素-血红素加氧酶复合物的EPR谱具有很强的轴向信号，g（平行）几乎等于6，g（垂直）几乎等于2。亚铁血红素-血红素加氧酶的(NO)-N-14和(NO)-N-15加合物分别表现出约20和约25高斯的EPR超细分裂。此外，两种亚硝基配合物都表现出与近端组氨酸氮自旋-自旋相互作用产生的约7高斯的额外超细分裂。血红素-血红素加氧酶-底物复合物中的血红素环境具有与肌红蛋白中的血红素相似的光谱特性。因此，在血红素片段的远端既没有像细胞色素P-450和过氧化物酶那样的强供电子的第五（近端）配体，也没有类似的吸电子网络。这一观察结果对本文讨论的血红素->胆绿素反应中氧活化过程的性质具有深远的意义。
The binding of ferrous and ferric hemes and manganese(II)- and manganese(III)-substituted hemes to heme oxygenase has been investigated by optical absorption, resonance Raman, and EPR spectroscopy. The results are consistent with the presence of a six-coordinate heme moiety ligated to an essential histidine ligand and a water molecule. The latter ionizes with a pK(a) almost-equal-to 8.0 to give a mixture of high-spin and low-spin six-coordinate hydroxo adducts. Addition of excess cyanide converts the heme to a hexacoordinate low-spin species. The resonance Raman spectrum of the ferrous heme-heme oxygenase complex and that of the Mn(II)protoporphyrin-heme oxygenase complex shows bands at 216 and 212 cm-1, respectively, that are assigned to the metal-histidine stretching mode. The EPR spectrum of the oxidized heme-heme oxygenase complex has a strongly axial signal with g(parallel-to) almost-equal-to 6 and g(perpendicular-to) almost-equal-to 2. (NO)-N-14 and (NO)-N-15 adducts of ferrous heme-heme oxygenase exhibit EPR hyperfine splittings of approximately 20 and approximately 25 Gauss, respectively. In addition, both nitrosyl complexes show additional superhyperfine splittings of approximately 7 Gauss from spin-spin interaction with the proximal histidine nitrogen. The heme environment in the heme-heme oxygenase enzyme-substrate complex has spectroscopic properties similar to those of the heme in myoglobin. Hence, there is neither a strongly electron-donating fifth (proximal) ligand nor an electron-withdrawing network on the distal side of the heme moiety comparable to that for cytochromes P-450 and peroxidases. This observation has profound implications about the nature of the oxygen-activating process in the heme --> biliverdin reaction that are discussed in this paper.