Nitric oxide binding

Goyal, M., Azizi, F., King, S. B., Kim-Shapiro, D. B., Nitric oxide binding to oxygenated hemoglobin under physiological conditions, Biochim. Biophys. Acta 1568 (2001), p. 252-260... 

Nitric oxide binds in the end on position to ferrous hemes, with the nitrogen atom facing the iron (Scheidt and Piciulo, 1976 Jameson et d., 1981 Peng and Ibers, 1976). It binds more tightly to ferrous iron, but has a greater ability than CO to bind to iron in the ferric state, producing a diamagnetic complex. Ferrous-NO complexes are reasonably stable compared to ferrous-02 complexes, but in many cases they can be oxidized or reduced. Nitric oxide is much more likely than CO to react at a metal site rather than to bind reversibly. 

Nitric oxide binds to the Cu(II) ion in the binuclear center of fully oxidized cytochrome oxidase (Brudvig et al., 1980). The binding of NO creates an even spin copper center and effectively breaks the spin coupling between the heme and copper metal ions. As a result, the high-spin heme EPR signal is visible at g = 6. 

Wanat A, Wolak M, Orzel L, Brindell M, van Eldik R, Stochel G. Laser flash photolysis as tool in the elucidation of the nitric oxide binding mechanism to metallobiomolecules. Coord Chem Rev 2002 229 37-49. 

Nitric Oxide Binding and Dissociation with Iron(III) Porphyrin Complex... 

Abu-Soud, H., Rousseau, DL, and Stuehr, DJ. 1996. Nitric oxide binding to the heme of neuronal nitric-oxide synthase links its activity to changes in oxygen tension. J. Biol. Chem. 271 32515-32518. 

In the late twentieth century, nitric oxide was revealed as a versatile biologically active molecule. For example, it has a significant role in regulating blood pressure. The mechanism by which it does this is not entirely clear but it has been proposed that nitric oxide binds to both the iron and to sulfur in haemoglobin. When nitric oxide bound to sulfur is transferred to receptors, the blood vessels dilate and this leads to a drop in blood pressure. In investigating the mechanism by which NO acts in biological systems, it is important to understand its electronic structure because this can tell us how it might bind to other molecules. 

Nitric oxide binds to deoxyhemocyanin, to deoxyhemerythrin, and to the mixed valence Fe Fe" semimethemerythrin. " Carbon monoxide binds to neither form of hemerythrin apparently the other ligands have insufficiently strong fields to stabilize the low-spin state for which electron density would be available for back donation into the CO tt orbitals. 

Nitric oxide binding to ferric cytochrome P450 A computational study. Inorg. Chem. 39, 2352-2359. 

Table 2 Kinetic and thennodynamic constants for nitric oxide binding to different forms of ferrous and ferric iron...

Ascenzi P, Coletta M et al (1994) Nitric oxide binding to ferrous native horse heart cytochrome c and to its carboxymethylated derivative A spectroscopic and thermodynamic study. J Inorg Biochem 53 273-280... 

Zhao Y, Hoganson C et al (1998) Structural changes in the heme proximal pocket induced by nitric oxide binding to soluble guanylate cyclase. Biochemistry 37 12458-12464... 

Nitric oxide binding to simpie iron(iii) porphyrin modeis... 

Nitric oxide binding to six-coordinate water-soluble iron(III) porphyrin complexes such as (TPPS" )Fe(H20)2, (TMPS" )Fe(H20)2, and... 

NO rate constants and activation parameters determined for nitric oxide binding to a five-coordinate monohydroxido species Fe (TMPS)(OH) (formed at pH > 6.9) (12) appear to be significandy smaller than those found for the (TMPS)Fe(H20)2 species (Table 1), clearly showing that NO coordination to Fe (TMPS)(OH) can no longer be controlled by the lability or accessibihty of the iron(III) center. In contrast to the mechanism of NO binding to iron(III) diaqua-ligated species, nitric oxide coordination to... 

In view of the strong a-donor and Jt-acceptor properties of the cyanide ligand, the effect of the latter on nitric oxide binding to (TMPS)Fe species has been mechanistically investigated (16). It was demonstrated that both cyanido complexes, viz., Fe "(TMPS)(CN)(H20) and Fe (TMPS) (CN)2, can react with NO leading to the formation of the same nitrosyl derivative, namely Fe (TMPS)(CN)(NO ). Due to very similar equihb-rium constants for the formation of Fe (TMPS)(CN)(H20) and Fe (TMPS)(CN)2, it was not possible to obtain a high yield of the monocyanido species at room temperature (as shown in Scheme 2 at low... 

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