tailieunhanh - Báo cáo khoa học: Open questions in ferredoxin-NADP+ reductase catalytic mechanism

Ferredoxin (flavodoxin)-NADP(H) reductases (FNR) are ubiquitous flavoenzymes that deliver NADPH or low potential one-electron donors (ferredoxin, flavodoxin) to redox-based metabolisms in plastids, mitochondria and bacteria. The plant-type reductase is also the basic prototype for one of the major families of flavin-containing electron transferases that display common functional and structural properties. | Eur. J. Biochem. 270 1900-1915 2003 FEBS 2003 doi REVIEW ARTICLE Open questions in ferredoxin-NADP reductase catalytic mechanism Nestor Carrillo and Eduardo A. Ceccarelli Molecular Biology Division Instituto de Biologia Molecular y Celular de Rosario IBR Facultad de Ciencias Bioquimicas y Farmaceuticas Universidad Nacional de Rosario Argentina Ferredoxin flavodoxin -NADP H reductases FNR are ubiquitous flavoenzymes that deliver NADPH or low potential one-electron donors ferredoxin flavodoxin to redox-based metabolisms in plastids mitochondria and bacteria. The plant-type reductase is also the basic prototype for one of the major families of flavin-containing electron transferases that display common functional and structural properties. Many aspects of FNR biochemistry have been extensively characterized in recent years using a combination of site-directed mutagenesis steady-state and transient kinetic experiments spectroscopy and X-ray crystallography. Despite these considerable advances various key features in the enzymology of these important reductases remain yet to be explained in molecular terms. This article reviews the current status of these open questions. Measurements of electron transfer rates and binding equilibria indicate that NADP H and ferredoxin interactions with FNR result in a reciprocal decrease of affinity and that this induced-fit step is a mandatory requisite for catalytic turnover. However the expected conformational movements are not apparent in the reported atomic structures of these flavoenzymes in the free state or in complex with their substrates. The overall reaction catalysed by FNR is freely reversible but the pathways leading to NADP or ferredoxin reduction proceed through entirely different kinetic mechanisms. Also the reductases isolated from various sources undergo inactivating denaturation on exposure to NADPH and other electron donors that reduce the FAD prosthetic group a phenomenon that might