Crystallization and preliminary X-ray diffraction studies of cytochrome c₆ from Porphyra yezoensis

Cytochrome c₆ from the red alga Porphyra yezoensis has been purified and crystallized by the sitting-drop vapour-diffusion method. Two different crystal forms, tetragonal and orthorhombic, were obtained. The tetragonal crystals belong to space group P4₁2₁2 or P4₃2₁2, with unit-cell dimensions a = 49.33 (2), c = 83.70 (10) Å. The orthorhombic crystals belong to space group P2₁2₁2₁, with unit-cell dimensions a = 46.74 (2), b = 49.42 (1), c = 37.11 (1) Å. Absorption spectra of the crystals showed that the tetragonal form was oxidized and the orthorhombic form was reduced.