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Ferredoxin-NADP+ Reductase.
- Source :
-
Journal of Biological Chemistry . 7/15/2005, Vol. 280 Issue 28, p25960-972. 13p. 3 Diagrams, 1 Chart, 9 Graphs. - Publication Year :
- 2005
-
Abstract
- The electron transfer cascade from photosystem I to NADP+ was studied at physiological pH by flash-absorption spectroscopy in a Synechocystis PCC6803 reconstituted system comprised of purified photosystem I, ferredoxin, and ferredoxin-NADP+ reductase. Experiments were conducted with a 34-kDa ferredoxin-NADP+ reductase homologous to the chloroplast enzyme and a 38-kDa N-terminal extended form. Small differences in kinetic and catalytic properties were found for these two forms, although the largest one has a 3-fold decreased affinity for ferredoxin. The dissociation rate of reduced ferredoxin from photosystem I (800 s-l) and the redox potential of the first reduction of ferredoxin-NADP+ reductase (-380 mV) were determined. In the absence of NADP+, differential absorption spectra support the existence of a high affinity complex between oxidized ferredoxin and semireduced ferredoxin-NADP+ reductase. An effective rate of 140–170 s-1 was also measured for the second reduction of ferredoxin-NADP+ reductase, this process having a rate constant similar to that of the first reduction. In the presence of NADP+, the second-order rate constant for the first reduction of ferredoxin-NADP+ reductase was 20% slower than in its absence, in line with the existence of ternary complexes (ferredoxin-NADP+ reductase)-NADP+-ferredoxin. A single catalytic turnover was monitored, with 50% NADP+ being reduced in 8–10 ms using 1.6 μM photosystem I. In conditions of multiple turnover, we determined initial rates of 360–410 electrons per s and per ferredoxin-NADP+ reductase for the reoxidation of 3.5 μM photoreduced ferredoxin. Identical rates were found with photosystem I lacking the PsaE subunit and wild type photosystem I. This suggests that, in contrast with previous proposals, the PsaE subunit is not involved in NADP+ photoreduction. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 00219258
- Volume :
- 280
- Issue :
- 28
- Database :
- Academic Search Index
- Journal :
- Journal of Biological Chemistry
- Publication Type :
- Academic Journal
- Accession number :
- 17745224
- Full Text :
- https://doi.org/10.1074/jbc.M503742200