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Published July 1994 | Published
Journal Article Open

Crystallization and X-ray Structure Determination of Cytochrome c_2 from Rhodobacter sphaeroides in Three Crystal Forms


Cytochrome c_2 serves as the secondary electron donor that reduces the photo-oxidized bacteriochlorophyll dimer in photosynthetic bacteria. Cytochrome c_2 from Rhodobacter sphaeroides has been crystallized in three different forms. At high ionic strength, crystals of a hexagonal space group (P6_122) were obtained, while at low ionic strength, triclinic (P1) and tetragonal (P4_12_12) crystals were formed. The three-dimensional structures of the cytochrome in all three crystal forms have been determined by X-ray diffraction at resolutions of 2.20 Å (hexagonal), 1.95 Å, (triclinic) and 1.53 Å (tetragonal). The most significant difference observed was the binding of an imidazole molecule to the iron atom of the heme group in the hexagonal structure. This binding displaces the sulfur atom of Met 100, which forms the axial ligand in the triclinic and tetragonal structures.

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© 1994 International Union of Crystallography. Received 15 November 1993; accepted 31 January 1994.

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