title: Single point mutation in the Rieske iron-sulfur subunit of cytochrome b6/f leads to an altered pH dependence of plastoquinol oxidation in Arabidopsis.
abstract: The pgr1 mutant of Arabidopsis thaliana carries a single point mutation (P194L) in the Rieske subunit of the cytochrome b6/f (cyt b6/f) complex and is characterised by a reduced electron transport activity at saturating light intensities in vivo. We have investigated the electron transport in this mutant under in vitro conditions. Measurements of P700 reduction kinetics and of photosynthetic electron transport rates indicated that electron transfer from cyt b6/f to photosystem I is not generally reduced in the mutant, but that the pH dependence of this reaction is altered. The data imply that the pH-dependent inactivation of electron transport through cyt b6/f is shifted by about 1 pH unit to more alkaline pH values in pgr1 thylakoids in comparison with wild-type thylakoids. This interpretation was confirmed by determination of the transmembrane deltapH at different stromal pH values showing that the lumen pH in pgr1 mutant plants cannot drop below pH 6 reflecting most likely a shift of the pK and/or the redox potential of the oxidised Rieske protein.
authors.affiliation: Plant Biochemistry, Heinrich-Heine-Universität Düsseldorf, Universitätsstr. 1, Düsseldorf, Germany. pjahns@uni-duesseldorf.de
authors.forename: Peter
authors.initials: P
authors.lastname: Jahns
authors.forename: Maria
authors.initials: M
authors.lastname: Graf
authors.forename: Yuri
authors.initials: Y
authors.lastname: Munekage
authors.forename: Toshiharu
authors.initials: T
authors.lastname: Shikanai
mesh_terms: D017360:Arabidopsis / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D002734:Chlorophyll / Q000378:metabolism; D003573:Cytochrome b Group / Q000235:genetics / Q000378:metabolism*; D045346:Cytochrome b6f Complex; D004579:Electron Transport / Q000502:physiology / Q000528:radiation effects; D014450:Electron Transport Complex III; D006863:Hydrogen-Ion Concentration / Q000528:radiation effects; D066298:In Vitro Techniques; D007506:Iron-Sulfur Proteins / Q000235:genetics / Q000378:metabolism*; D008027:Light; D045342:Light-Harvesting Protein Complexes; D010084:Oxidation-Reduction; D010788:Photosynthesis / Q000502:physiology / Q000528:radiation effects; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism / Q000528:radiation effects; D045331:Photosystem I Protein Complex; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D010971:Plastoquinone / Q000031:analogs & derivatives* / Q000378:metabolism*; D017354:Point Mutation; D021122:Protein Subunits; D020524:Thylakoids / Q000737:chemistry / Q000378:metabolism / Q000528:radiation effects
chemical_list: D003573:Cytochrome b Group; D007506:Iron-Sulfur Proteins; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D010940:Plant Proteins; D021122:Protein Subunits; C037989:Rieske iron-sulfur protein; D002734:Chlorophyll; C003165:plastoquinol; C001785:chlorophyll P 700; D045346:Cytochrome b6f Complex; D014450:Electron Transport Complex III; D010971:Plastoquinone