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Respective roles of the ferredoxin :NADP-oxidoreductase isoforms in the cyanobacterium Synechocystis sp. PCC 6803

Anja Korn 1
1 LPB - Photocatalyse et Biohydrogène
B3S - Département Biochimie, Biophysique et Biologie Structurale
Abstract : In photosynthetic organisms, ferredoxin:NADP oxidoreductase (FNR) provides NADPH for CO2 assimilation, but it also utilizes NADPH to provide reduced ferredoxin (Fd). The cyanobacterium Synechocystis sp. strain PCC6803 contains two FNR isoforms, a small (FNRS, 34 kDa) and a large one (FNRL, 46 kDa) that is associated with the phycobilisome (PBS), a light-harvesting complex. We purified a PBS subcomplex comprising FNRL (FNRL-PC) and compared the enzymatic properties of FNRL-PC to FNRS. FNRL-PC exhibits an increased NADPH affinity, and a decreased Fd affinity in agreement with its predicted lower activity of Fd reduction. FNRL-PC shows also a decrease in the rate of single electron transfer (ET) from Fdred. Most of the obtained differences are attributed to steric hindrance by the phycocyanin moiety of FNRL-PC. Both isoforms seem to catalyze the NADP+ reduction under multiple turnover conditions to the same extent and we obtained evidence that, under our high ionic strength conditions, ET from Fdred is rate limiting. During in vivo studies, we presented evidence supporting an increase of NADPH oxidation by respiratory or cyclic ET in a mutant lacking FNRL and a similar behavior was observed for the wild type under low CO2. The measurements clearly showed that FNRS is implicated in this alternative ET and we propose that FNRS attaches to NDH-1 acting as the dehydrogenase module. FNR localization and/or substrate availability seem to be essential so that FNR isoforms perform their respective roles in vivo. Future studies should result in a more complete in vivo view and clarify the important issue of the NADPH-dependent ET into the PQ pool that seems to be enhanced in the absence of FNRL.
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Submitted on : Friday, February 26, 2010 - 2:56:44 PM
Last modification on : Wednesday, October 14, 2020 - 3:49:20 AM
Long-term archiving on: : Friday, June 18, 2010 - 9:58:38 PM

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  • HAL Id : tel-00460234, version 1

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Anja Korn. Respective roles of the ferredoxin :NADP-oxidoreductase isoforms in the cyanobacterium Synechocystis sp. PCC 6803. Biological Physics [physics.bio-ph]. Université Paris Sud - Paris XI, 2010. English. ⟨tel-00460234⟩

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