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short communications
Cytochrome c4 from the bacterium Pseudomonas stutzeri has been crystallized and X-ray diffraction data have been collected to 2.2 Å resolution. The crystals belong to the monoclinic system, space group P21 with cell parameters a = 49.49, b = 58.58, c = 63.51 Å and β = 96.96°. The crystals contain two molecules it, the asymmetric unit. Cytochrome c4 is known to contain two covalently bound haem groups per molecule and positions of the four haem Fe atoms in the asymmetric unit were determined from native anomalous-dispersion differences. The shortest Fe–Fe distances found in the crystal were 15.8, 16.9 and 19.0 Å.