Spectroscopic investigation and determination of reactivity and structure of the tetraheme cytochrome c(3) from Desulfovibrio desulfuricans Essex 6

Cytochrome c(3), a small (14-kDa) soluble tetraheme protein was isolated fr om the periplasmic fraction of Desulfovibrio desulfuricans strain Essex 6. Its major physiological function appears to be that of an electron carrier for the periplasmic hydrogenase. It has been also shown to interact with th e high-molecular-mass cytochrome complex in the cytoplasmic membrane, which eventually feeds electrons into the membraneous quinone pool, as well as w ith the membrane-associated dissimilatory sulfite reductase. The EPR spectr a show features of four different low-spin Fe(III) hemes. Orthorhombic crys tals of cytochrome c(3) were obtained and X-ray diffraction data were colle cted to below 2 Angstrom resolution. The structure was solved by molecular replacement using cytochrome c(3) from D. desulfuricans ATCC 27774 as a sea rch model.