Fluorescence Studies on Ferredoxin-NADP Reductase

Abstract

Abstract With highly purified preparations of ferredoxin-NADP reductase (EC 1.6.99.4; also EC 1.6.1.1) from spinach chloroplasts a strong flavin fluorescence was observed (excitation at 450 nm). At pH 7.0, the fluorescence was approximately 40% higher than that of free FAD. Pure reductase from the heterokont alga Bumilleriopsis had only a fluorescence of less than 5% of that of the spinach protein. Essentially the same low fluorescence was found with impure spinach reductase preparations. The low-fluorescent samples of both species exhibited about the same quenching response to salts and buffers which differed from the highly fluorescent spinach flavoprotein preparation. The low fluorescence of the algal protein could be enhanced by NADP, but not by ferredoxin. Maximum fluorescence increase was observed when reductase and NADP were present in a 1:1 molar ratio. Ferredoxin did not counteract the reductase are hereby substantiated.