Kinetics of substrate inhibition of periplasmic nitrate reductase |
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Authors: | Julien G.J. Jacques,Bé né dicte Burlat,Pascal Arnoux,Monique Sabaty,Bruno Guigliarelli,Christophe Lé ger,David Pignol,Vincent Fourmond |
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Affiliation: | 1. Aix-Marseille Université, CNRS, BIP UMR 7281, 31 Chemin J. Aiguier, F-13402 Marseille Cedex 20, France;2. Aix-Marseille Université, CNRS, CEA, DSV/IBEB/LBC UMR 7265, F-13108 Saint Paul Lez Durance, France |
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Abstract: | Periplasmic nitrate reductase catalyzes the reduction of nitrate into nitrite using a mononuclear molybdenum cofactor that has nearly the same structure in all enzymes of the DMSO reductase family. In previous electrochemical investigations, we found that the enzyme exists in several inactive states, some of which may have been previously isolated and mistaken for catalytic intermediates. In particular, the enzyme slowly and reversibly inactivates when exposed to high concentrations of nitrate. Here, we study the kinetics of substrate inhibition and its dependence on electrode potential and substrate concentration to learn about the properties of the active and inactive forms of the enzyme. We conclude that the substrate-inhibited enzyme never significantly accumulates in the EPR-active Mo(+ V) state. This conclusion is relevant to spectroscopic investigations where attempts are made to trap a Mo(+ V) catalytic intermediate using high concentrations of nitrate. |
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Keywords: | Enzyme kinetics Nitrate reductase Electrochemistry EPR spectroscopy |
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