Oxidation of a Ferrocytochrome c in the Crystalline State—Structural Change and Anion Binding

It was found that crystalline bonito heart ferrocytochrome c was oxidized without significant change of the crystal lattice. The difference Fourier syntheses between oxidized and reduced crystals were calculated at 4 and 3 Å resolutions. The Fourier maps show that the ferricytochrome c obtained here captures a sulfate anion in the vicinity of the side chains of Lys (99) and Glu (61). The anion binding was anticipated on the basis of biochemical experiments. In other regions, no significant structural change was observed, though on oxidation in solution some drastic conformational changes have been reported. This fact suggests that the mechanism of oxidation in the crystalline state may be different from that in solution.