Orientations of Iron-Sulfur Clusters FA and FB in the Homodimeric Type-I Photosynthetic Reaction Center of Heliobacterium modesticaldum.
Orientations of the FA and FB iron-sulfur (FeS) clusters in a structure-unknown type-I homodimeric heriobacterial reaction center (hRC) were studied in oriented membranes of the thermophilic anaerobic photosynthetic bacterium Heliobacterium modesticaldum by electron paramagnetic resonance (EPR), and compared with those in heterodimeric photosystem I (PS I). The Rieske-type FeS center in the cytochrome b/c complex showed a well-oriented EPR signal. Illumination at 14 K induced an FB(-) signal with g-axes of gz = 2.066, gy = 1.937, and gx = 1.890, tilted at angles of 60°, 60°, and 45°, respectively, with respect to the membrane normal. Chemical reduction with dithionite produced an additional signal of FA(-), which magnetically interacted with FB(-), with gz = 2.046, gy = 1.942, and gx = 1.911 at 30°, 60°, and 90°, respectively. The angles and redox properties of FA(-) and FB(-) in hRC resemble those of FB(-) and FA(-), respectively, in PS I. Therefore, FA and FB in hRC, named after their g-value similarities, seem to be located like FB and FA, not like FA and FB, respectively, in PS I. The reducing side of hRC could resemble those in PS I, if the names of FA and FB are interchanged with each other.
Division of Material Science (Physics), Graduate School of Science, Nagoya University , Furocho, Chikusa, Nagoya 464-8602, Japan.
Toru
T
Kondo
Department of Biological Sciences, Graduate School of Science, Osaka University , Osaka 560-0043, Japan.
Masahiro
M
Matsuoka
Department of Biological Sciences, Graduate School of Science, Osaka University , Osaka 560-0043, Japan.
Chihiro
C
Azai
Center for Gene Research, Nagoya University , Furocho, Chikusa, Nagoya 464-8602, Japan.
Shigeru
S
Itoh
Department of Biological Sciences, Graduate School of Science, Osaka University , Osaka 560-0043, Japan.
Hirozo
H
Oh-Oka
D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D000068016:Eubacteriales / Q000378:metabolism*; D019281:Dimerization; D004578:Electron Spin Resonance Spectroscopy; D007506:Iron-Sulfur Proteins / Q000737:chemistry* / Q000378:metabolism; D010084:Oxidation-Reduction; D045331:Photosystem I Protein Complex / Q000737:chemistry* / Q000378:metabolism
D001426:Bacterial Proteins; D007506:Iron-Sulfur Proteins; D045331:Photosystem I Protein Complex