The molecular mechanism of mammalian NO-synthases: A story of electrons and protons

• Published in: Journal of inorganic biochemistry Vol. 105; no. 2; pp. 127 - 141
• Main Author: Santolini, Jérôme
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.02.2011
• Subjects: Activation; Animals; Coenzymes - chemistry; Electron transfer; Electrons; Heme - chemistry; Heme - metabolism; Humans; Iron - chemistry; Molecular mechanism; Nitric Oxide - biosynthesis; Nitric oxide synthase; Nitric Oxide Synthase - chemistry; Nitric Oxide Synthase - metabolism; Oxygen; Oxygen - chemistry; Protein Binding; Proton transfer; Protons; Pterins - chemistry; Superoxides - chemistry; Electron transfer; Nitric oxide synthase; Oxygen; Activation; Molecular mechanism; Proton transfer
• ISSN: 0162-0134; 1873-3344; 1873-3344
• DOI: 10.1016/j.jinorgbio.2010.10.011

Since its discovery, nitric oxide synthase (NOS), the enzyme responsible for NO biosynthesis in mammals, has been the subject of extensive investigations regarding its catalytic and molecular mechanisms. These studies reveal the high degree of sophistication of NOS functioning and regulation. However, the precise description of the NOS molecular mechanism and in particular of the oxygen activation chemistry is still lacking. The reaction intermediates implicated in NOS catalysis continue to elude identification and the current working paradigm is increasingly contested. Consequently, the last three years has seen the emergence of several competing models. All these models propose the same global reaction scheme consisting of two successive oxidation reactions but they diverge in the details of their reaction sequence. The major discrepancies concern the number, source and characteristics of proton and electron transfer processes. As a result each model proposes distinct reaction pathways with different implied oxidative species. This review aims to examine the different experimental evidence concerning NOS proton and electron transfer events and the role played by the substrates and cofactors in these processes. The resulting discussion should provide a comparative picture of all potential models for the NOS molecular mechanism. The precise description of the NOS molecular mechanism of nitric oxide synthase and of the oxygen activation chemistry is still lacking. The major discrepancies between the different mechanism models concern the number, source and characteristics of proton and electron transfer processes, leading to distinct reaction pathways and oxidative species. This review aims to examine the experimental evidence concerning NOS proton and electron transfers and the role played by the substrates and cofactors in these processes. [Display omitted]