Preliminary X-ray studies of the tetra-heme cytochromec3and the octa-heme cytochromec3fromDesulfovibrio gigas

Abstract
A tetra-heme and an octa-heme cytochrome c3 from the sulfate bacterium Desulfovibrio gigas have been crystallized. Diffraction quality crystals of the tetra-heme cytochrome are obtained from solution by the addition of polyethylene glycol at pH 6.5. The crystals are orthorhombic, space group P21212 with unit cell parameters a = 42.27 Å, b = 52.54 Å and c = 52.83 Å. The octa-heme cytochrome crystals develop from low ionic strength solutions of phosphate or Tris-Cl in the pH range 6.2–7.6. The crystals belong to the trigonal system, space group P31 or the enantiomorph P32, with unit cell parameters a = b = 57.4 Å, c = 97.3 Å, γ = 120°. Single crystal diffraction studies of the structures of these two low-potential cytochromes are in progress