title: Type 1 reaction center of photosynthetic heliobacteria.
abstract: The reaction center (RC) of heliobacteria contains iron-sulfur centers as terminal electron acceptors, analogous to those of green sulfur bacteria as well as photosystem I in cyanobacteria and higher plants. Therefore, they all belong to the so-called type 1 RCs, in contrast to the type 2 RCs of purple bacteria and photosystem II containing quinone molecules. Although the architecture of the heliobacterial RC as a protein complex is still unknown, it forms a homodimer made up of two identical PshA core proteins, where two symmetrical electron transfer pathways along the C2 axis are assumed to be equally functional. Electrons are considered to be transferred from membrane-bound cytochrome c (PetJ) to a special pair P800, a chlorophyll a-like molecule A0, (a quinone molecule A1) and a [4Fe-4S] center Fx and, finally, to 2[4Fe-4S] centers FA/FB. No definite evidence has been obtained for the presence of functional quinone acceptor A1. An additional interesting point is that the electron transfer reaction from cytochrome c to P800 proceeds in a collisional mode. It is highly dependent on the temperature, ion strength and/or viscosity in a reaction medium, suggesting that a heme-binding moiety fluctuates in an aqueous phase with its amino-terminus anchored to membranes.
authors.affiliation: Department of Biological Sciences, Graduate School of Science, Osaka University, Osaka, Japan. ohoka@bio.sci.osaka-u.ac.jp
authors.forename: Hirozo
authors.initials: H
authors.lastname: Oh-oka
mesh_terms: D000595:Amino Acid Sequence; D001419:Bacteria / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D016227:Benzoquinones / Q000737:chemistry / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D019414:Chlorobi / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D000458:Cyanobacteria / Q000378:metabolism; D045304:Cytochromes c / Q000378:metabolism; D004579:Electron Transport; D007506:Iron-Sulfur Proteins / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D009994:Osmolar Concentration; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry / Q000378:metabolism*; D045331:Photosystem I Protein Complex / Q000737:chemistry / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000378:metabolism; D013696:Temperature; D014783:Viscosity
chemical_list: D001426:Bacterial Proteins; D016227:Benzoquinones; D007506:Iron-Sulfur Proteins; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; C096017:PscA protein, green sulfur bacteria; D002734:Chlorophyll; C004532:quinone; D045304:Cytochromes c; D000077194:Chlorophyll A