The electron spin distribution in nitrosylhemoglobin

Doetschman, David C.; Schwartz, S.A.; Utterback, S. G.

doi:10.1016/0301-0104(80)85032-4

Cited by 9 publications

(3 citation statements)

References 17 publications

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“…It seems that the Fe-NO bond strength will depend on the relative importance of the cr-electronic system (which is maximized at about 120°) and x-back-bonding, which maximizes at 180° ( Cotton & Wilkinson, 1980). ESR results for heme-FenNO systems place 53% of the unpaired spin population in the x*(NO) level (Doetschman et al, 1980), clearly demonstrating the mixing between x*z(NO) and d*z(Fe).…”

Section: Resultsmentioning

confidence: 94%

Nitrosyliron(III) hemoglobin: autoreduction and spectroscopy

Addison¹,

Stephanos²

1986

Biochemistry

107

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Nitrosyl complexes of the iron(III) forms of myoglobin, human hemoglobin, Glycera dibranchiata hemoglobins (Hbm and Hbh), and model iron(II) and iron(III) synthetic porphyrins including octaethylporphyrin (OEP) have been prepared. The iron(III) heme proteins are electron spin (paramagnetic) resonance (ESR) silent, while hexacoordinate solution structures are indicated for [Fe(OEP)(NO)2]ClO4 and for Hbm(II)NO, which has an ESR spectrum similar to that of Mb(II)NO and the hexacoordinate iron(II) model complex Fe(OEP)NO(BzIm). The splitting of the alpha- and beta-bands in the optical spectrum of Mb(III)NO and Hbh(III)NO contrasts markedly with the sharp, single bands observed in that of Hbm-(III)NO. The nondegeneracy of the dxz and dyz orbitals in Mb(III)NO and Hbh(III)NO is attributed to the influence of the distal histidine. Circular dichroism spectra were obtained for Hbm(III)NO, Hbm(II)NO, Hbh(III)NO, Hbh(II)NO, Mb(II)NO, and Mb(III)NO. The vicinal chiral center contribution that governs the heme protein CD leads to low Kuhn anisotropies, which have been used to assign certain electronic transitions. The Hb(III)NO spectrum is not stable but transforms into that of Hb(II)NO. This autoredox process follows kinetics that are first order in FeIIINO. The relative rates of autoreduction (25 degrees C, 1 atm NO) are Mb(III)NO less than Hbm(III)NO less than Hb alpha(III)NO less than HbA(III)NO. At high NO partial pressure or after "recycling" of HbA, the rates of reduction decrease. The first step in the reaction of NO with the ferric heme is the reversible formation of the formally iron(III) adduct. This reacts with another molecule of NO, generating the final heme(II)-NO via nitrosylation of NO itself or of an endogenous nucleophile. Kinetic and spectroscopic evidence shows involvement of trans-heme-(NO)2 in the reaction. The activation parameters delta H and delta S were determined. The overall reaction is photoenhanced.

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Section: Resultsmentioning

confidence: 94%

Nitrosyliron(III) hemoglobin: autoreduction and spectroscopy

Addison¹,

Stephanos²

1986

Biochemistry

107

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“…Here, the resulting ferrous heme-nitrosyl complexes, which are ls-{FeNO} 7 species, are very stable and show characteristic electron paramagnetic resonance (EPR) spectra with S t = 1/2 ground states and characteristic hyperfine couplings with the N atom of the coordinated NO (see Section ). − In addition, the obtained EPR spectra are also characteristic of the coordination number of the formed heme–NO adduct (either 5C or 6C), and in this way, provide further insight into the properties of the heme’s proximal ligand in the protein . In contrast, the corresponding O 2 adducts of ferrous hemes are diamagnetic and EPR silent.…”

Section: Introductionmentioning

confidence: 89%

The Biologically Relevant Coordination Chemistry of Iron and Nitric Oxide: Electronic Structure and Reactivity

et al. 2021

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Nitric oxide (NO) is an important signaling molecule that is involved in a wide range of physiological and pathological events in biology. Metal coordination chemistry, especially with iron, is at the heart of many biological transformations involving NO. A series of heme proteins, nitric oxide synthases (NOS), soluble guanylate cyclase (sGC), and nitrophorins, are responsible for the biosynthesis, sensing, and transport of NO. Alternatively, NO can be generated from nitrite by heme- and copper-containing nitrite reductases (NIRs). The NO-bearing small molecules such as nitrosothiols and dinitrosyl iron complexes (DNICs) can serve as an alternative vehicle for NO storage and transport. Once NO is formed, the rich reaction chemistry of NO leads to a wide variety of biological activities including reduction of NO by heme or non-heme iron-containing NO reductases and protein post-translational modifications by DNICs. Much of our understanding of the reactivity of metal sites in biology with NO and the mechanisms of these transformations has come from the elucidation of the geometric and electronic structures and chemical reactivity of synthetic model systems, in synergy with biochemical and biophysical studies on the relevant proteins themselves. This review focuses on recent advancements from studies on proteins and model complexes that not only have improved our understanding of the biological roles of NO but also have provided foundations for biomedical research and for bio-inspired catalyst design in energy science.

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“…Because the electron spin density is distributed mainly over three atoms (Fe 2ϩ ,N(NO), N ⑀ (His-F8)) in a known fashion, we simplify the analysis, calculating the position of a reduced spin center (Wells and Makinen, 1988;. We consider the spin-density distribution of the complex, with 70% of spin density on the Fe 2ϩ , 23% on the N(NO), and 7% on the N ⑀ (His-F8) (Doetschman et al, 1980;Utterback et al, 1983). In the axial symmetry the reduced spin center is 0.25 Å from iron in the g ʈ direction, and in the rhombic symmetry it is 0.25 Å from iron in the g z direction, in both cases above the heme.…”

Section: Methodsmentioning

confidence: 99%

Proton Electron Nuclear Double Resonance from Nitrosyl Horse Heart Myoglobin: The Role of His-E7 and Val-E11

Flores

Wajnberg

Bemski

2000

Biophysical Journal

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Electron nuclear double resonance (ENDOR) spectroscopy has been used to study protons in nitrosyl horse heart myoglobin (MbNO). (1)H ENDOR spectra were recorded for different settings of the magnetic field. Detailed analysis of the ENDOR powder spectra, using computer simulation, based on the "orientation-selection" principle, leads to the identification of the available protons in the heme pocket. We observe hyperfine interactions of the N(HisF8)-Fe(2+)-N(NO) complex with five protons in axial and with eight protons in the rhombic symmetry along different orientations, including those of the principal axes of the g-tensor. Protons from His-E7 and Val-E11 residues are identified in the two symmetries, rhombic and axial, exhibited by MbNO. Our results indicate that both residues are present inside the heme pocket and help to stabilize one particular conformation.

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The electron spin distribution in nitrosylhemoglobin

Cited by 9 publications

References 17 publications

Nitrosyliron(III) hemoglobin: autoreduction and spectroscopy

Nitrosyliron(III) hemoglobin: autoreduction and spectroscopy

The Biologically Relevant Coordination Chemistry of Iron and Nitric Oxide: Electronic Structure and Reactivity

Proton Electron Nuclear Double Resonance from Nitrosyl Horse Heart Myoglobin: The Role of His-E7 and Val-E11

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