The reduction by dithionite of Fe(III) myoglobin derivatives with different ligands attached to the iron atom. A study by rapid-wavelength-scanning stopped-flow spectrophotometry.
The reduction by dithionite of Fe(III) myoglobin derivatives with different ligands attached to the iron atom. A study by rapid-wavelength-scanning stopped-flow spectrophotometry.
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通过连二亚硫酸盐还原铁原子上连接有不同配体的 Fe(III) 肌红蛋白衍生物。
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发表时间：
1977
期刊：
影响因子：
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通讯作者：
M. Hollaway
中科院分区：
文献类型：
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作者：
R. P. Cox;M. Hollaway
1.用快速波长扫描停流分光光度法研究了在pH为6.4的磷酸盐缓冲溶液中，连二亚硫酸钠对抹香鲸Fe(III)肌红蛋白配体络合物的还原作用。配体为叠氮、氰化物、氟化物、咪唑、硫氰酸盐和水。2.铁(III)-肌红蛋白氰化物的还原导致了铁(II)-肌红蛋白氰化物的瞬时生成，但在其他衍生物的还原过程中没有观察到中间物种。在所有病例中，反应的最终产物是未连接的Fe(II)肌红蛋白。3.考察了二亚硫酸盐浓度对还原速率的影响，表明SO2-离子是叠氮、氰化物、氟化物和硫氰酸盐衍生物还原的活性物种。4.将观察到的不同配体浓度下的还原速率与预测的涉及配体先前解离的还原途径的还原速率进行比较，使我们能够估计在配体处于适当位置时的还原速率(外球还原)。外球还原的相对速率变化较大，顺序为咪唑>CN->SCN->N3->F-。氟化物对外球还原的抵抗力很强，与SO2-的反应在还原前只通过F-的解离途径进行。据计算，该络合物的任何直接还原都至少比叠氮衍生物慢100倍。5.根据血红素蛋白中轴向配基的可能位置对结果进行了讨论，认为电子到达Fe(III)中心的途径可能是通过这些配基的PPI轨道。
1. The reductions of a number of sperm whale Fe(III) myoglobin-ligand complexes by sodium dithionite in a phosphate buffer pH 6.4, were investigated by using rapid-wavelength-scanning stopped-flow spectrophotometry. The ligands were azide, cyanide, fluoride, imidazole, thiocyanate and water. 2. The reduction of Fe(III) myoglobin cyanide led to the transient formation of Fe(II) myoglobin cyanide but no intermediate species were observable during the reductions of the other derivatives. The final product of the reaction in all cases was unliganded Fe(II)myoglobin. 3. Invesigation of the effect of dithionite concentration on the rate of reduction indicated that the SO2- radical ion was the active species in reducing the azide, cyanide, fluoride and thiocyanate derivatives. 4. Comparison of the observed rates of reduction at different ligand concentrations with those predicted for a pathway of reduction involving prior dissociation of the ligand, allowed us to estimate the rate of reduction with the ligand in position (outer-sphere reduction). There was a large variation in the relative rates of outer-sphere reduction in the order imidazole greater than CN- greater than SCN- greater than N3- greater than F-. The fluoride derivative was so resistant to outer-sphere reduction that the reaction with SO2- proceeded only by a pathway involving dissociation of F- before reduction. It was calculated that any direct reduction of this complex was at least 100 times slower than that of the azide derivative. 5. The results are discussed in terms of the possible rôle of the axial ligands in haem proteins and it is suggested that the pathway of the electron to the Fe(III) centre may be via the ppi orbitals of these ligands.