Publication: A Density Functional Theory Investigation on the Mechanism of the Second Half-Reaction of Nitric Oxide Synthase

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Title	A Density Functional Theory Investigation on the Mechanism of the Second Half-Reaction of Nitric Oxide Synthase
Authors/Editors*	J. J. Robinet, K.-B. Cho, J. W. Gauld
Where published*	J. Am. Chem. Soc.
How published*	Journal
Year*	2008
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Abstract	Density functional theory methods have been employed to systematically investigate the overall mechanism of the second half-reaction of nitric oxide synthases. The initial heme-bound hydrogen peroxide intermediate previously identified is found to first undergo a simple rotation about its O—O peroxide bond. Then, via a 'ping-pong' peroxidase-like mechanism the –OinH– proton is transferred back onto the substrate's –NO oxygen then subsequently onto the outer oxygen of the resulting Feheme–OOH species. As a result Oout is released as H2O with concomitant formation of a Compound I-type (Feheme–O) species. Formation of the final citrulline and NO products can then be achieved in one step via a tetrahedral transition structure resulting from direct attack of the Feheme–O moiety at the substrates guanidinium carbon centre. The possible role of alternative mechanisms involving a protonated Compound II-type species or an initial transfer of only the –NH– hydrogen of the =NHOH+ group of NHA is also discussed.

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