Ferrous heme-nitrosyls

The higher stability of ferrous heme nitrosyl complexes compared to the corresponding ferric species is well documented [see Refs (44-46, 69) for reviews]. Since cytochrome P450, catalase, and cytochrome c oxidase are commonly associated with reducing agents, a mechanism exists for longer term inhibition of the activity of these proteins. 

Due to the many biological functions of ferrous heme nitrosyls, many corresponding model complexes have been synthesized and structurally and spectroscopically characterized, viz. tetraphenylporphyrin (TPPH2), octaethylporphyrin (OEPH2) and protoporphyrin IX diester (PPDEH2), ms o-tetrakis (4-carboxyphenyl) porphyrin (TCPP), meso-tetrakis [4-(N,N,N-trimethyl) aminophenyl] porphyrin (TTMAPP),... 

Sulok CD, Bauer JL et al (2012) A detailed investigation into the electronic structures of macrocyclic iron (Il)-nitrosyl compounds and their similarities to ferrous heme-nitrosyls. Inorg Chim Acta 380 148-160... 

Lehnert N, Galinato MG et al (2010) Nuclear resonance vibrational spectroscopy applied to [Fe (OEP) (NO)] the vibrational assignments of five-coordinate ferrous heme-nitrosyls and implications for electronic structure, hiorg Chem 49 4133-4148... 

Paulat F, Berio TC et al (2008) Vibrational assignments of six-coordinate ferrous heme nitrosyls new insight from nuclear resmiance vibrational spectroscopy, friorg Chem 47 11449 11451... 

Lehnert N (2008) Chapter 6 - EPR and low-temperature MCD spectroscopy of ferrous heme nitrosyls. In Abhik G (ed) The smallest biomolecules diatomics and their interactions with heme proteins. Elsevier, Amsterdam... 

Table II shows the same results for the nitrosyl ferrous heme complex at Fe-NO 1.743 and 2.143 A. The singly occupied orbital (79) has primarily NO n and a character with both d and d 2 contributions. Although this orbital is deeply buried, as can be seen from its energy, it is shown between the doubly occupied and virtual orbitals for convenience. For comparison, the ground-state molecular orbitals of carbonyl-(44) and oxyheme (45) complexes are shown in Table III.

Table II. Ground State Orbital Description of Nitrosyl Ferrous Heme at Fe NO Distances of 1.743 A and 2.143 A...

Figure 2. Simplified, scaled, dlagramatlc representation of the excited-state energies of nitrosyl ferrous heme complex at iron-nitrogen distances of 1.743, 1,943, 2.143 and 2.343 A showing correlation between similar photodissociating states. The 71 71 transition of the Soret and Q bands are also identified.

The major conclusion of the present study, as can be seen in Figures 1 and 2, is that the primary photodissociating states, in both nitrosyl ferrous and ferric heme complexes correspond to the d - d 2 excitations. The calculated energies also indicate that this dissociative channel can be activated independent of the excitation frequency in the range of Q to Soret band energies. This is the same type of excitation previously identified as the photoactive state involved in CO and O2 photodissociation from ferrous heme complexes. 

Ground-state molecular orbitals carbonyl-carbonylheme oxyheme complexes, 5,11-12t nitrosyl ferrous heme complexes, 5... 

Nitrosyl ferrous heme complexes See also Nitrosoheme complexes geometry, 4... 

The pink cured meat pigment mononitrosylhemochrome is a complex of nitric oxide (NO), ferrous heme iron, and heat-denatured globin protein (Table F3.2.1). The pink nitrosylheme (NO-heme) moiety may be extracted from the protein in aqueous acetone and quantitated by A540 (see Basic Protocol 1). The percent nitrosylation may be determined from measurement of ppm NO-heme relative to ppm total acid hematin (hemin) extracted in acidified acetone (see Basic Protocol 2), since NO-heme is completely oxidized to hemin in acid solution (i.e., 1 ppm NO-heme = 1 ppm hemin). 

Resonance Raman studies of CO and NO bound to PaNiR showed unusually high stretching frequencies compared with other hemoproteins due to the different electronic properties of d heme." Nitrite binds to heme d in both ferrous and ferric oxidation states but has a higher affinity for ferrous Fe with Aid values of approximately IpM and 2.5mM, respectively. Extensive evidence for the formation of an electrophilic heme-nitrosyl species derived from nitrite (formulated as Fe -NO" " or Fe" -NO) based on isotope exchange with 0-labeled water into NO, nitrosyl transfer to N nucleophiles, and FTIR studies of the interaction of NO with oxidized PsNiR." In the latter study a band at l,910cm was assigned to a ferric NO heme complex. This species is considered as the key intermediate in the mechanism for nitrite reduction." ... 

Morse RH, Chan SI (1980) Electron paramagnetic resonance studies of nitrosyl ferrous heme complexes. Determination of an equilibrium between two conformations. J Biol Chem... 

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