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Reduction of Photosystem I Reaction Center in DrgA Mutant of the Cyanobacterium Synechocystis sp. PCC 6803 Lacking Soluble NAD(P)H:Quinone Oxidoreductase

I. V. Elanskaya1*, K. N. Timofeev2, V. G. Grivennikova3, G. V. Kuznetsova1, L. N. Davletshina2, E. P. Lukashev2, and F. V. Yaminsky2

1Department of Genetics, 2Department of Biophysics, and 3Department of Biochemistry, Faculty of Biology, Lomonosov Moscow State University, Moscow 119992, Russia; fax: (7-095) 939-2957; E-mail: ivelanskaya@mail.ru

* To whom correspondence should be addressed.

Received July 7, 2003; Revision received August 20, 2003
Photoautotrophically grown cells of the cyanobacterium Synechocystis sp. PCC 6803 wild type and the Ins2 mutant carrying an insertion in the drgA gene encoding soluble NAD(P)H:quinone oxidoreductase (NQR) did not differ in the rate of light-induced oxygen evolution and Photosystem I reaction center (P700+) reduction after its oxidation with a white light pulse. In the presence of DCMU, the rate of P700+ reduction was lower in mutant cells than in wild type cells. Depletion of respiratory substrates after 24 h dark-starvation caused more potent decrease in the rate of P700+ reduction in DrgA mutant cells than in wild type cells. The reduction of P700+ by electrons derived from exogenous glucose was slower in photoautotrophically grown DrgA mutant than in wild type cells. The mutation in the drgA gene did not impair the ability of Synechocystis sp. PCC 6803 cells to oxidize glucose under heterotrophic conditions and did not impair the NDH-1-dependent, rotenone-inhibited electron transfer from NADPH to P700+ in thylakoid membranes of the cyanobacterium. Under photoautotrophic growth conditions, NADPH-dehydrogenase activity in DrgA mutant cells was less than 30% from the level observed in wild type cells. The results suggest that NQR, encoded by the drgA gene, might participate in the regulation of cytoplasmic NADPH oxidation, supplying NADP+ for glucose oxidation in the pentose phosphate cycle of cyanobacteria.
KEY WORDS: cyanobacterium Synechocystis sp. PCC 6803, drgA gene, NAD(P)H:quinone oxidoreductase, NAD(P)H-dehydrogenase, Photosystem I, EPR spectroscopy