Human neuronal nitric oxide synthase can catalyze one-electron reduction of adriamycin: role of flavin domain.
We have analyzed the mechanism of one-electron reduction of adriamycin (Adr) using recombinant full-length human neuronal nitric-oxide synthase and its flavin domains. Both enzymes catalyzed aerobic NADPH oxidation in the presence of Adr. Calcium/calmodulin (Ca(2+)/CaM) stimulated the NADPH oxidation of Adr. In the presence or absence of Ca(2+)/CaM, the flavin semiquinone radical species were major intermediates observed during the oxidation of the reduced enzyme by Adr. The FAD-NADPH binding domain did not significantly catalyze the reduction of Adr. Neither the FAD semiquinone (FADH*) nor the air-stable semiquinone (FAD-FMNH*) reacted rapidly with Adr. These data indicate that the fully reduced species of FMN (FMNH(2)) donates one electron to Adr, and that the rate of Adr reduction is stimulated by a rapid electron exchange between the two flavins in the presence of Ca(2+)/CaM. Based on these findings, we propose a role for the FAD-FMN pair in the one-electron reduction of Adr.
Fu
Jie
J
Department of Life Science, Graduate School of Science, Himeji Institute of Technology, Harima Science Garden City, Hyogo 678-1297, Japan.
Yamamoto
Keita
K
Guan
Zhi-Wen
ZW
Kimura
Shigenobu
S
Iyanagi
Takashi
T
D002118:Calcium / Q000737:chemistry*; D002147:Calmodulin / Q000737:chemistry*; D002384:Catalysis; D002478:Cells, Cultured; D004317:Doxorubicin / Q000737:chemistry*; D004579:Electron Transport; D005415:Flavins / Q000737:chemistry*; D006801:Humans; D007700:Kinetics; D009474:Neurons / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000737:chemistry*; D010084:Oxidation-Reduction; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry
D002147:Calmodulin; D005415:Flavins; D011994:Recombinant Proteins; D004317:Doxorubicin; D019001:Nitric Oxide Synthase; D002118:Calcium