title: Oxygen activation in NO synthases: evidence for a direct role of the substrate.
abstract: Nitric oxide (NO) and the other reactive nitrogen species (RNOS) play crucial patho-physiological roles at the interface of oxidative stress and signalling processes. In mammals, the NO synthases (NOSs) are the source of these reactive nitrogen species, and so to understand the precise biological role of RNOS and NO requires elucidation of the molecular functioning of NOS. Oxygen activation, which is at the core of NOS catalysis, involves a sophisticated sequence of electron and proton transfers. While electron transfer in NOS has received much attention, the proton transfer processes has been scarcely investigated. Here, we report an original approach that combines fast-kinetic techniques coupled to resonance Raman spectroscopy with the use of synthetic analogues of NOS substrate. We characterise Fe(II)-O2 reaction intermediates in the presence of L-arginine (Arg), alkyl- and aryl-guanidines. The presence of new reaction intermediates, such as ferric haem-peroxide, that was formerly postulated, was tracked by analysing the oxygen activation reaction at different times and with different excitation wavelengths. Our results suggest that Arg is not a proton donor, but indirectly intervenes in oxygen activation mechanism by modulating the distal H-bond network and, in particular, by tuning the position and the role of the distal water molecule. This report supports a catalytic model with two proton transfers in step 1 (Arg hydroxylation) but only one proton transfer in step 2 (N(ω)-hydroxy-L-arginine oxidation).
authors.affiliation: Laboratoire Stress Oxydant et Détoxication Institute for Integrative Biology of the Cell (I2BC) CEA, CNRS, Université Paris-Saclay Gif-sur-Yvette Cedex France.
authors.forename: Albane
authors.initials: A
authors.lastname: Brunel
authors.affiliation: Département de biochimie, de microbiologie et de bio-informatique, and PROTEO Pavillon Charles-Eugène Marchand Université Laval Québec Canada.
authors.forename: Jérôme
authors.initials: J
authors.lastname: Lang
authors.affiliation: Département de biochimie, de microbiologie et de bio-informatique, and PROTEO Pavillon Charles-Eugène Marchand Université Laval Québec Canada.
authors.forename: Manon
authors.initials: M
authors.lastname: Couture
authors.affiliation: UMR 8601 CNRS-University Paris Descartes Paris France.
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Boucher
authors.affiliation: Laboratoire Stress Oxydant et Détoxication Institute for Integrative Biology of the Cell (I2BC) CEA, CNRS, Université Paris-Saclay Gif-sur-Yvette Cedex France.
authors.forename: Pierre
authors.initials: P
authors.lastname: Dorlet
authors.affiliation: Laboratoire Stress Oxydant et Détoxication Institute for Integrative Biology of the Cell (I2BC) CEA, CNRS, Université Paris-Saclay Gif-sur-Yvette Cedex France.
authors.forename: Jérôme
authors.initials: J
authors.lastname: Santolini
keywords: kinetics; mechanism; nitric oxide synthase; oxygen activation; resonance Raman spectroscopy