EPR study of the structure and spin distribution at the binding site in human nitrosylhemoglobin single crystalsa)

Utterback, S. G.; Doetschman, David C.; Szumowski, Jerzy; Rizos, Apostolos K.

doi:10.1063/1.444606

Cited by 24 publications

(14 citation statements)

References 19 publications

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“…For the six-coordinated structure, θ Fe - N - O =115° as observed recently for MbNO was used, while other values determined by X-ray structural analysis of Fe II −porphyrin-NOs 41a,b (θ Fe - N - O = 142° for six-coordinated complex and 149° for five-coordinated complex) and of Hb−NO were not so satisfactory as shown in Table with regard to reproduction of the observed Δ( 15 N 16 O) and Δ( 15 N 18 O). These X-ray values of θ Fe - N - O are larger than the EPR values: 137° for Hb(α)−NO, 130° for Hb(β)−NO; 153° for Mb−NO at 293 K, and 109° for Mb−NO at 77 K . The calculated results for MbNO at pH 4 were obtained with θ Fe - N - O =130°.…”

Section: Discussionmentioning

confidence: 64%

Resonance Raman Investigation of Fe−N−O Structure of Nitrosylheme in Myoglobin and Its Mutants

et al. 1999

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Resonance Raman spectra have been observed for NO adducts of wild-type (WT) sperm whale myoglobin (MbNO) and its H64G, H64L, L29W, V68W, and V68T mutants at neutral and acidic pH. Raman excitation in resonance with the Soret band enabled us to detect the Fe−NO stretching (νFe - NO), N−O stretching (νNO), and Fe−N−O bending (δFeNO) bands. The νFe - NO, δFeNO, and νNO bands of WT MbNO at neutral pH were observed at 560, 452, and 1613 cm-1, respectively, and substitution of the distal His64 to Gly or Leu caused an upshift of νNO to 1631−1635 cm-1 but no change in νFe - NO. This change in νNO is considered to be due to the removal of hydrogen bonding between His64 and bound NO. Conversely, substitution of Leu29 with tryptophan (L29W) altered νFe - NO but caused no change in νNO at neutral pH. This feature resembles that of MbO2 but distinctly differs from that of MbCO, for which the Fe−CO and C−O stretching frequencies have an inverse linear correlation. The change in νFe - NO for L29W−MbNO is probably caused by tilting of the Fe−N bond from the heme normal on account of steric hindrance from the large indole ring but would not be due to changes in the Fe−N−O bond angle. When pH is lowered to 4, MbNO adopts the five-coordinate structure due to cleavage of the Fe−His bond. Accordingly, the heme maker bands such as ν3 and ν10, shifted from 1500 and 1636 cm-1 at pH 7.4 to 1509 and 1646 cm-1 at pH 4 which are in agreement with those of a five-coordinate Fe−protoporphyrin−NO complex in detergent micelles at neutral pH. The νFe - NO and νNO bands of acidic MbNO were observed at 520 and 1668 cm-1 and exhibited no shift when the distal His was replaced by Gly or Leu. The latter observation supports previous X-ray crystallographic, infrared, and resonance Raman spectroscopic measurements which show that the distal histidine becomes protonated at pH 4 and swings out into the solvent away from the bound ligand.

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Section: Discussionmentioning

confidence: 64%

Resonance Raman Investigation of Fe−N−O Structure of Nitrosylheme in Myoglobin and Its Mutants

et al. 1999

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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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“…In the 6C case, a nine-line hyperfine pattern is observed for g mid with typical N-donor ligands bound trans to NO, resulting from strong coupling of the unpaired electron with the 14 N nucleus of NO, and weaker coupling with the 14 N nucleus of the axially-bound heterocycle (Figure ). ,, This difference between the 5C and 6C complexes can be explained by analyzing the single crystal EPR data of 6C Mb(II)−NO and Hb(II)–NO , in comparison to those of the 5C model complex [Fe(OEP)(NO)], and further correlating these results with DFT calculations . The DFT results show that in the 5C case, the principal axis of g min is closest to the Fe–NO bond vector, while in the 6C case the g tensor is rotated, with the principal axis of the medium g-value, g mid , now closest to the Fe–NO axis (see Figure ).…”

Section: Nitric Oxide In Mammalian Signaling and Immune Defensementioning

confidence: 99%

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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EPR study of the structure and spin distribution at the binding site in human nitrosylhemoglobin single crystalsa)

Cited by 24 publications

References 19 publications

Resonance Raman Investigation of Fe−N−O Structure of Nitrosylheme in Myoglobin and Its Mutants

Resonance Raman Investigation of Fe−N−O Structure of Nitrosylheme in Myoglobin and Its Mutants

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

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

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