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Arch Microbiol. 2000 May-Jun;173(5-6):333-8.

The bidirectional hydrogenase of Synechocystis sp. PCC 6803 works as an electron valve during photosynthesis.

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FB Biologie/Botanik, Philipps-Universität, Marburg, Germany.


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.

[Indexed for MEDLINE]

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