Hegetschweiler K, Saltman P, Dalvit C, Wright P E
Biochim Biophys Acta. 1987 Apr 30;912(3):384-97. doi: 10.1016/0167-4838(87)90043-4.
Two distinct mechanisms by which sperm whale myoglobin reduces, respectively, complexes of Fe(III) and Cu(II) and, in turn, is oxidized to metmyoglobin have been characterized. For both mechanisms, deoxymyoglobin is the active reductant. An outer sphere electron transfer, probably at the edge of the heme, is involved for Fe(III)NTA (NTA is nitrilotriacetic acid). This pathway does not involve ionic binding of the Fe(III) complex to the protein. The most reactive species of Fe(III)NTA is uncharged. No inhibition is observed with Ni(II) or Zn(II). An outer sphere site specific electron transfer is operative for reduction of Cu(II) complexes. The site has been characterized using NMR spectroscopy and involves one or more histidines. There is an initial binding of the Cu(II) chelate. The ternary complex of chelator-Cu(II)-deoxymyoglobin is a mandatory intermediate. Ni(II) and Zn(II) compete with Cu(II) for the binding site. A scheme for the participation of either or both of these mechanisms in reduction reactions of heme proteins is proposed. Both the overall redox potential, delta E0, and the stability constant for the ternary complex, K, govern the pathway and the reaction rate.
抹香鲸肌红蛋白分别还原Fe(III)和Cu(II)配合物进而被氧化为高铁肌红蛋白的两种不同机制已得到表征。对于这两种机制，脱氧肌红蛋白都是活性还原剂。对于Fe(III)NTA（NTA是次氮基三乙酸），涉及一种外层电子转移，可能发生在血红素边缘。该途径不涉及Fe(III)配合物与蛋白质的离子结合。Fe(III)NTA的最活泼物种是不带电荷的。未观察到Ni(II)或Zn(II)的抑制作用。一种外层位点特异性电子转移作用于Cu(II)配合物的还原。该位点已通过核磁共振光谱进行表征，涉及一个或多个组氨酸。Cu(II)螯合物存在初始结合。螯合剂-Cu(II)-脱氧肌红蛋白的三元配合物是一个必需的中间体。Ni(II)和Zn(II)与Cu(II)竞争结合位点。提出了这两种机制中的一种或两种参与血红素蛋白还原反应的方案。整体氧化还原电位ΔE0和三元配合物的稳定常数K都决定了途径和反应速率。
