title: The bidirectional hydrogenase of Synechocystis sp. PCC 6803 works as an electron valve during photosynthesis.
abstract: The activity of the bidirectional hydrogenase of the cyanobacterium Synechocystis sp. PCC 6803 was found not to be regulated in parallel to respiration but to photosynthesis. A mutant with a deletion in the large hydrogenase subunit gene (hoxH), which contains the active site, was impaired in the oxidation of photosystem I (PSI) when illuminated with light, which excites either PSI alone or both photosystems. The fluorescence of photosystem II (PSII) of this mutant was higher than that of wild-type cells. The transcript level of the photosynthetic genes psbA, psaA and petB was found to be different in the hydrogenase-free mutant cells compared to wild-type cells, which indicates that the hydrogenase has an effect on the regulation of these genes. Collectively, these results suggest that the bidirectional hydrogenase functions as a valve for low-potential electrons generated during the light reaction of photosynthesis, thus preventing a slowing down of electron transport. This conclusion is supported by growth curves demonstrating that the mutant cells need more time to adapt to changing light intensities. Investigations of the wild-type and deltahoxH strains strongly suggest that Synechocystis contains only the bidirectional hydrogenase, which seems to be essentially insensitive to oxygen.
authors.affiliation: FB Biologie/Botanik, Philipps-Universität, Marburg, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Appel
authors.forename: S
authors.initials: S
authors.lastname: Phunpruch
authors.forename: K
authors.initials: K
authors.lastname: Steinmüller
authors.forename: R
authors.initials: R
authors.lastname: Schulz
mesh_terms: D015152:Blotting, Northern; D002462:Cell Membrane; D002734:Chlorophyll / Q000378:metabolism; D000458:Cyanobacteria / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D004579:Electron Transport; D006859:Hydrogen / Q000378:metabolism; D015151:Immunoblotting; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D010101:Oxygen Consumption; D010788:Photosynthesis
chemical_list: D002734:Chlorophyll; C001785:chlorophyll P 700; D006859:Hydrogen; D010088:Oxidoreductases; C021376:hydrogen dehydrogenase