Wüthrich K
Proc Natl Acad Sci U S A. 1969 Aug;63(4):1071-8. doi: 10.1073/pnas.63.4.1071.
In cytochrome c the axial positions of the heme iron are occupied by two amino acid residues, one of which is known from X-ray studies to be histidyl. Nuclear magnetic resonance spectroscopy provides strong evidence that the sixth ligand is a methionyl residue in both the ferric and ferrous oxidation states. It is further shown that in cyanoferricytochrome c cyanide ion replaces methionyl in the first coordination sphere of the heme iron. Additional data are obtained on the protein conformation and on the electronic structure of the heme group in ferricytochrome c. As in other heme proteins, the interactions with the polypeptide chain greatly affect the unpaired electron distribution in the heme group of cytochrome c. In particular, from a comparison of ferricytochrome c and cyanoferricytochrome c, the importance of the coordination of the sixth ligand is apparent.
在细胞色素c中，血红素铁的轴向位置被两个氨基酸残基占据，其中一个通过X射线研究已知为组氨酸残基。核磁共振光谱提供了有力证据，表明在三价铁和二价铁氧化态下，第六个配体都是甲硫氨酸残基。进一步表明，在氰化高铁细胞色素c中，氰离子在血红素铁的第一配位层中取代了甲硫氨酸。还获得了关于高铁细胞色素c中蛋白质构象和血红素基团电子结构的其他数据。与其他血红素蛋白一样，与多肽链的相互作用极大地影响了细胞色素c血红素基团中未成对电子的分布。特别是，通过比较高铁细胞色素c和氰化高铁细胞色素c，第六个配体配位的重要性显而易见。
