Ferredoxin-NADP⁺ oxidoreductase is the respiratory NADPH dehydrogenase of the cyanobacterium Anabaena variabilis

The NADPH dehydrogenase of the cyanobacterium Anabaena variabilis was solubilized, purified, and characterized. Activity staining after nondenaturing polyacrylamide gel electrophoresis, kinetics, and immunological characterization led to the conclusion that only one thylakoid-associated NADPH dehydrogenase exists in Anabaena, identical with ferredoxin-NADP⁺ oxidoreductase (FNR). After sodium dodecyl sulfatepolyacrylamide gel electrophoresis an intense band at 34 kDa and a weak band at 52 kDa were found by immunoblotting with an antibody against Anabaena FNR. Using a cellfree preparation competent of oxidative phosphorylation it was demonstrated that FNR operates as a respiratory NADPH dehydrogenase coupled to cyanide-sensitive oxidative ATP formation.