Abstract
Ferredoxin-NAD(P)+ oxidoreductases (FNRs) of photoautotroph Chlorobaculum tepidum (CtFNR) and heterotroph Bacillus subtilis (BsFNR) are homo-dimeric flavoprotein exhibiting a significant conservation of structural topology with bacterial NADPH-thioredoxin reductase. Although the redox reaction catalyzed by FNR is theoretically reversible, under the physiological conditions the direction of the reaction is assumed to be optimized toward either NADP+ reduction in photosynthetic process or NADPH oxidation in non-photosynthetic one. In this presentation the directionality of the redox reactions with NADP+/H and the structure-function relationships will be discussed based on the pre-steady-state kinetics. NADPH oxidation and NADP+ reduction reactions by BsFNR occurred with rapid formations of charge transfer complexes (CTCs) followed by the rate-limiting hydride transfer. The rate of the NADPH oxidation direction in the hydride transfer step was much faster than that of NADP+ reduction direction (500 s−1 vs. < 10 s−1), indicating NADPH oxidation was favored in BsFNR-catalyzing reaction. The deletions of the C-terminal amino acid residues almost did not affect the directionality. NADPH oxidation by CtFNR yielded a rapid formation of CTCs followedby the rate-limiting hydride transfer. The amount of reduced CtFNR at the equilibrium was in part even in the presence of ∼50-fold excess NADPH. NADP+ reduction by CtFNR provided no charge transfer band and the observed rate for the NADP+ reduction by CtFNR was rather slow (∼ 5 s−1), suggesting the formation of CTC was the rate-limiting. The hydride transfer rates in both directions were estimated to be comparable, indicating redox reaction with NADP+/H was reversible in the case of CtFNR. The depletion of the C-terminal residues turns out CtFNR to be NADPH oxidizing enzyme, suggesting that the C-terminal residues are required for tuning the redox properties of the FAD prosthetic group.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.