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[14] Rubredoxin in crystalline state

1994; Academic Press; Linguagem: Inglês

10.1016/0076-6879(94)43016-0

1557-7988

Larry C. Sieker, Ronald E. Stenkamp, Jean LeGall,

Photosynthetic Processes and Mechanisms

This chapter focuses on rubredoxin (Rd) in crystalline state, which is regarded as one of the simplest iron proteins. Rds are composed of 45 to 54 amino-acid residues with molecular weights ranging from 5000 to 6000 and contain one iron atom liganded by four cysteine residues. The iron center can be reversibly reduced at a redox potential near 0 mV. Rds are divided into three categories: (1) Rds from sulfate-reducing Desulfovibrio species, (2) Rds from a mixed assortment of bacteria, and (3) thermophilic Rds. The redox potentials of Rds isolated from sulfate-reducing bacteria (SRB) are relatively high. The amino-acid sequences of all rubredoxins show two sets of the -C-x-y-C-G-z- sequence around the iron center, where each cysteine is a ligand to the iron atom. Lys-46 is the only invariant hydrophilic residue in all the Rds. Except for the Desulfovibrio vulgaris (D. vulgaris) Rd structure, the crystal structures of the other Rds show that Lys-46 extends across to the neighboring chain, making an H bond to the carbonyl oxygens of residue 30 and residue 33, presumably contributing to the stability of the molecule.