Conversion of mitochondrial cytochrome b5 into a species capable of performing the efficient coupled oxidation of heme.
Conversion of mitochondrial cytochrome b5 into a species capable of performing the efficient coupled oxidation of heme.
复制标题
将线粒体细胞色素 b5 转化为能够进行血红素有效偶联氧化的物质。
DOI：
10.1021/bi9809324
复制
发表时间：
1998
期刊：
影响因子：
2.9
通讯作者：
Rivera,M
中科院分区：
文献类型：
--
作者：
Rodríguez,JC;Rivera,M
组氨酸 63 是线粒体外膜细胞色素 b5 (OM cytb5) 中的血红素轴向配体之一，已被蛋氨酸取代。 H63M 变体对血红素进行有效的区域选择性耦合氧化，以产生 >90% 的绿血红素 α-异构体。通过电子、EPR 和 NMR 光谱研究对该变体进行了表征，表明三价铁形式是一种高自旋物种，其血红素在近端位点由组氨酸 39 协调，并且可能在远端位点由水协调。根据核磁共振波谱研究，排除了蛋氨酸与铁血红素的配位。将咪唑添加到三价铁变体的溶液中会导致形成由咪唑和组氨酸 63 轴向配位的物质。发现在不存在外源咪唑的情况下该变体的还原电位为+110 mV，在存在咪唑的情况下该变体的还原电位为-92 mV。这些值分别与肌红蛋白 (50 mV) 和野生型 OM cytb5 (-102 mV) 的还原电位相比较，与上述轴向结扎一致。另一方面，亚铁变体是一种由组氨酸 39 和蛋氨酸 63 协调的低自旋物种。一氧化碳 (CO) 很容易将 Met-63 从其在亚铁血红素上的配位位点取代，而 CO 不能完全从其在绿血红素上的配位位点取代 Met-63。因此，H63M 变体中绿血红素氧化为铁胆绿素的抑制机制似乎与 CO 存在下血红素-血红素加氧酶复合物观察到的机制相似。
Histidine-63, one of the heme axial ligands in outer mitochondrial membrane cytochromeb5(OM cytb5) has been replaced by a methionine. The H63M variant performs the efficient and regioselective coupled oxidation of heme in order to produce >90% of the α-isomer of verdoheme. The variant was characterized by electronic, EPR, and NMR spectroscopic studies which indicate that the ferric form is a high-spin species whose heme is coordinated by histidine-39 in the proximal site and likely by water in the distal site. The coordination of methionine to the ferric heme was ruled out on the basis of NMR spectroscopic studies. Addition of imidazole to a solution of the ferric variant results in the formation of a species axially coordinated by imidazole and histidine-63. The reduction potential of the variant was found to be +110 mV in the absence of exogenous imidazole and −92 mV in the presence of imidazole. These values compare well with the reduction potential of myoglobin (50 mV) and wild-type OM cytb5(−102 mV), respectively, consistent with the axial ligation described above. The ferrous variant, on the other hand, is a low-spin species coordinated by histidine-39 and methionine-63. Carbon monoxide (CO) readily displaces Met-63 from its coordination site on the ferrous heme, whereas CO cannot completely displace Met-63 from its coordination site on verdoheme. Consequently, the mechanism of inhibition for the oxidation of verdoheme to iron-biliverdin in the H63M variant appears to be similar to that observed for the heme−heme oxygenase complex in the presence of CO.