Abstract
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 p2H dependence in the range of p2 4.8–10.0.

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