title: Electron transfer in the heliobacterial reaction center: evidence against a quinone-type electron acceptor functioning analogous to A1 in photosystem I.
abstract: Membrane fragments from Heliobacillus mobilis were characterized using time resolved optical spectroscopy and photovoltage measurements in order to detect a possible participation of menaquinone (MQ), functioning analogous to the phylloquinone A1 in photosystem I, as intermediate in electron transfer from the primary acceptor A0 to the iron-sulfur cluster FX in the photosynthetic reaction center. The spectroscopic data obtained exclude that electron transfer from a semiquinone anion MQ- to FX occurred in the time window from 2 ns to 4 micros, where it would be expected in analogy to photosystem I. In the case of a prereduction of FX, only the primary pair P798+A0- was formed. The photovoltage data yielded a single kinetic phase with a time constant of 700 ps for the transmembrane electron transfer beyond A0; the relative amplitude of this phase suggests that it reflects electron transfer from A0- to FX.
authors.affiliation: Section de Bioénergétique, DBCM, CEA and CNRS URA 2096, Centre d'Etudes de Saclay, 91191 Gif-sur-Yvette Cedex, France. brettel@dsvidf.cea.fr
authors.forename: K
authors.initials: K
authors.lastname: Brettel
authors.forename: W
authors.initials: W
authors.lastname: Leibl
authors.forename: U
authors.initials: U
authors.lastname: Liebl
mesh_terms: D001419:Bacteria / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D004579:Electron Transport; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism*; D014812:Vitamin K / Q000378:metabolism
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins; D014812:Vitamin K