title: Synechocystis ferredoxin-NADP(+) oxidoreductase is capable of functioning as ferric reductase and of driving the Fenton reaction in the absence or presence of free flavin.
abstract: We purified free flavin-independent NADPH oxidoreductase from Synechocystis sp. PCC6803 based on NADPH oxidation activity elicited during reduction of t-butyl hydroperoxide in the presence of Fe(III)-EDTA. The N-terminal sequencing of the purified enzyme revealed it to be ferredoxin-NADP(+) oxidoreductase (FNR( S )). The purified enzyme reacted with cytochrome c, ferricyanide and 2,6-dichloroindophenol (DCIP). The substrate specificity of the enzyme was similar to the known FNR. DNA degradation occurring in the presence of NADPH, Fe(III)-EDTA and hydrogen peroxide was potently enhanced by the purified enzyme, indicating that Synechocystis FNR( S ) may drive the Fenton reaction. The Fenton reaction by Synechocystis FNR( S ) in the presence of natural chelate iron compounds tended to be considerably lower than that in the presence of synthetic chelate iron compounds. The Synechocystis FNR( S ) is considered to reduce ferric iron to ferrous iron when it evokes the Fenton reaction. Although Synechocystis FNR( S ) was able to reduce iron compounds in the absence of free flavin, the ferric reduction by the enzyme was enhanced by the addition of free flavin. The enhancement was detected not only in the presence of natural chelate iron compounds but also synthetic chelate iron compounds.
authors.affiliation: The Department of Bioscience, Tokyo University of Agriculture, 1-1-1 Sakuragaoka, Setagaya-ku, Tokyo, 156-8502, Japan.
authors.forename: Junichi
authors.initials: J
authors.lastname: Sato
authors.forename: Kouji
authors.initials: K
authors.lastname: Takeda
authors.forename: Rika
authors.initials: R
authors.lastname: Nishiyama
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Watanabe
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Abo
authors.forename: Etsuro
authors.initials: E
authors.lastname: Yoshimura
authors.forename: Junichi
authors.initials: J
authors.lastname: Nakagawa
authors.forename: Akira
authors.initials: A
authors.lastname: Abe
authors.forename: Shinji
authors.initials: S
authors.lastname: Kawasaki
authors.forename: Youichi
authors.initials: Y
authors.lastname: Niimura
mesh_terms: D038181:FMN Reductase / Q000378:metabolism*; D005287:Ferredoxin-NADP Reductase / Q000235:genetics / Q000378:metabolism*; D005415:Flavins / Q000378:metabolism*; D013379:Substrate Specificity; D046939:Synechocystis / Q000201:enzymology* / Q000378:metabolism*
chemical_list: D005415:Flavins; D005287:Ferredoxin-NADP Reductase; D038181:FMN Reductase; C023903:ferric citrate iron reductase