Non-equivalent natures of the coordinated imidazole rings of cytochrome c3 from D. vulgaris Miyazaki F as studied by 1H NMR

All of the C2 proton signals of the coordinated histidine residues in the 1H NMR spectrum of cytochrome c 3 from D. vulgaris Miyuzaki F were assigned by specific deuteration. They appeared at extremely high fields and scattered in a wide range from −4 to −22 ppm. This clearly shows that the chemical properties of the imidazole groups are quite different from one another. The extremely high-field shift of the C2 signal indicates that some of them must carry the imidazolate-like nature to some extent. This might be responsible for the extremely low redox potentials of the four hemes. On changing temperature, most of them showed Curie-type change. All of the C2 signals showed a small p 2H dependence in the range of p 2 4.8–10.0.