Nuclear magnetic resonance investigation of the electronic structure of deoxymyoglobin

Mar, Gerd N. La; Davis, Nicolette L.; Johnson, Robert D.; Smith, Wanda S.; Hauksson, Jón; Budd, David L.; Dalichow, Frank; Langry, Kevin C.; Morris, Ian K.; Smith, Kevin M.

doi:10.1021/ja00063a003

Cited by 21 publications

(25 citation statements)

References 3 publications

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“…Considering the δ para values of ∼30 and ∼10 ppm for the 2-CF 3 and 8-CF 3 signals of deoxy Mb(2,8-DPF), respectively, these signals exhibited relatively large splitting, i.e., a shift difference of 20.61 ppm at 25 °C. As reported previously, , this finding indicated the significant contribution of the π spin delocalization mechanism of the high-spin quintet heme Fe(II) in the 5 E state. Similarly, the relatively large splitting, i.e., ∼20 ppm, for the relatively small δ para values, i.e., up to ∼30 ppm, for signals m and M of deoxy Mb(7-PF) were also consistent with the 5 E ground state.…”

Section: Discussionsupporting

confidence: 88%

“…In the case of the 2-CF 3 and 8-CF 3 signals of deoxy Mb(2,8-DPF), δ c due to unpaired electron density delocalized through the d xz and d yz orbitals of the heme Fe is thought to dominate their δ para values. With the d-electron configuration of the 5 E state, i.e., (d xy )(d xz ) 2 (d yz )(d z 2 )(d x 2 – y 2 ), π spin delocalization primarily occurs at pyrroles I, III over II, IV (the coordinate system is shown in Figure A) . Although, the π spin delocalization in the 5 E state is possibly perturbed by weak Jahn–Teller distortion, the preferential delocalization toward pyrroles I, III over II, IV is maintained.…”

Section: Discussionmentioning

confidence: 99%

“…Theoretical studies indicated that the low-lying electronic terms of the high-spin heme Fe(II) in deoxy Mb are 5 B 2 , 5 E , 3 E , and 1 A with 5 B 2 or one of the 5 E components as the ground state (Figure B). − Investigation of the Mössbauer effect of deoxy Mb demonstrated that the ground state is one of the components of the 5 E term split by rhombic distortions . The d-orbital splittings derived from the 5 E , (d xy )(d xz ) 2 (d yz )(d z 2 )(d x 2 – y 2 ) or (d xy )(d xz )(d yz ) 2 (d z 2 )(d x 2 – y 2 ), and 5 B 2 , (d xy ) 2 (d xz )(d yz )(d z 2 )(d x 2 – y 2 ) states for the high-spin heme Fe(II) are thought to be close in terms of energy. − In addition, in the 5 E state, the relative energies of the d xz and d yz orbitals are affected by the interaction between the heme Fe d π orbital and His93 N ε out-of-plane p orbital, leading to the removal of the degeneracy of the energy levels for the two configurations of the 5 E term. − With the orientation of the His93 side chain imidazole with respect to the heme cofactor, as illustrated in Figure A, the energy level of (d xy )(d xz ) 2 (d yz )(d z 2 )(d x 2 – y 2 ) is lower than that of (d xy )(d xz )(d yz ) 2 (d z 2 )(d x 2 – y 2 ). The contributions of the multiple electronic states to the electronic and magnetic natures of deoxy Mb involve complicated data interpretation.…”

Section: Introductionmentioning

confidence: 99%

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Characterization of Ground State Electron Configurations of High-Spin Quintet Ferrous Heme Iron in Deoxy Myoglobin Reconstituted with Trifluoromethyl Group-Substituted Heme Cofactors

et al. 2016

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We introduced trifluoromethyl (CF) group(s) as heme side chain(s) of sperm whale myoglobin (Mb) in order to characterize the electronic nature of heme Fe(II) in deoxy Mb using F NMR spectroscopy. On the basis of the anti-Curie behavior of CF signals, we found that the deoxy Mb is in thermal equilibrium between the B, (d)(d)(d)(d)(d), and E, (d)(d)(d)(d)(d), states of the heme Fe(II), i.e., B ⇆ E. Analysis of the curvature in Curie plots has yielded for the first time ΔH and ΔS values of ∼-20 kJ mol and ∼-60 J K mol, respectively, for the thermal equilibrium. Thus, the E state is slightly dominant over theB one at 25 °C. These findings provide not only valuable information about the ground state electronic structure of the high-spin heme Fe(II) in deoxy native Mb but also an important clue for elucidating the mechanism responsible for acceleration of the spin-forbidden oxygenation of the protein.

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Section: Discussionsupporting

confidence: 88%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Characterization of Ground State Electron Configurations of High-Spin Quintet Ferrous Heme Iron in Deoxy Myoglobin Reconstituted with Trifluoromethyl Group-Substituted Heme Cofactors

et al. 2016

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“…In contrast, unligated Fe (II) Mb (deoxygenated Mb) shows no detectable interaction with PA. PA does not perturb any detectable signals from the heme 5CH 3 , 6Hα propionate, 4Hα vinyl, 2Hα vinyl, and 7 Hα propionate, as observed in the hyperfine shifted 10–15 ppm spectral region [6,39]. No hyperfine shifted signals in the upfield region appear perturbed.…”

Section: Discussionmentioning

confidence: 96%

Palmitate interaction with physiological states of myoglobin

Shih

Chung

Sriram

et al. 2014

Biochimica et Biophysica Acta (BBA) - General Subjects

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Background Previous studies have shown that palmitate (PA) can bind specifically and non-specifically to Fe (III) MbCN. The present study has observed PA interaction with physiological states of Fe (II) Mb, and the observations support the hypothesis that Mb may have a potential role in facilitating intracellular fatty acid transport. Methods 1H NMR spectra measurements of the Mb signal during PA titration show signal changes consistent with specific and non-specific binding. Results Palmitate (PA) interacts differently with physiological states of Mb. Deoxy Mb does not interact specifically or non-specifically with PA, while the carbonmonoxy myoglobin (MbCO) interaction with PA decreases the intensity of selective signals and produces a 0.15 ppm upfield shift of the PA methylene peak. The selective signal change upon PA titration provides a basis to determine an apparent PA binding constant, which serves to create a model comparing the competitive PA binding and facilitated fatty acid transport of Mb and fatty acid binding protein (FABP). Conclusions Given contrasting PA interaction of ligated vs. unligated Mb, the cellular fatty acid binding protein (FABP) and Mb concentration in the cell, the reported cellular diffusion coefficients, the PA dissociation constants from ligated Mb and FABP, a fatty acid flux model suggests that Mb can compete with FABP transporting cellular fatty acid. General Significance Under oxygenated conditions and continuous energy demand, Mb, dependent fatty acid transport could influence the cell’s preference for carbohydrate or fatty acid as a fuel source and regulate fatty acid metabolism.

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“…Chemical shifts of axial His ligand nuclei have been used to probe the imidazolate character and hydrogen bonding interactions in heme model complexes and in peroxidase and globin heme proteins 4,6–7,24,55,68. Banci and coworkers demonstrated that the chemical shifts of proximal His protons Hε1 and Hδ1 in CN − -ligated derivatives correlate to reduction potentials observed of horseradish peroxidase (HRP), cytochrome c peroxidase (C c P) and lignin peroxidase (LiP).…”

Section: Discussionmentioning

confidence: 99%

Variation and Analysis of Second-Sphere Interactions and Axial Histidinate Character inc-type Cytochromes

Bowman

Bren

2010

Inorg. Chem.

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The electron-donating properties of the axial His ligand to heme iron in cytochromes c (cyts c) are found to be correlated with midpoint reduction potential (E m ) in variants of Hydrogenobacter thermophilus cytochrome c 552 (Ht cyt c 552 ) in which mutations have been made in and near the Cys-X-X-Cys-His (CXXCH) heme-binding motif. To probe the strength of the His-Fe(III) interaction, we have measured 13 C nuclear magnetic resonance (NMR) chemical shifts for 13 CN − bound to heme iron trans to the axial His in Ht Fe(III) cyt c 552 variants. We observe a linear relationship between these 13 C chemical shifts and E m , indicating that the His-Fe(III) bond strength correlates with E m . To probe a conserved hydrogen bonding interaction between the axial His Hδ1 and the backbone carbonyl of a Pro residue, we measured the pK a of the axial His Hδ1 proton (pK a(2) ), which we propose to relate to the His-Fe(III) interaction, reduction potential and local electrostatic effects. The observed linear relationship between the axial His 13 Cβ chemical shift and E m is proposed to reflect histidinate (anionic) character of the ligand. A linear relationship also is seen between the average heme methyl 1 H chemical shift and E m which may reflect variation in axial His electron-donating properties or in the ruffling distortion of the heme plane. In summary, chemical shifts of the axial His and exogenous CN − bound trans to His are shown to be sensitive probes of the His-Fe(III) interaction in variants of Ht cyt c 552 and display trends that correlate with E m .

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Nuclear magnetic resonance investigation of the electronic structure of deoxymyoglobin

Cited by 21 publications

References 3 publications

Characterization of Ground State Electron Configurations of High-Spin Quintet Ferrous Heme Iron in Deoxy Myoglobin Reconstituted with Trifluoromethyl Group-Substituted Heme Cofactors

Characterization of Ground State Electron Configurations of High-Spin Quintet Ferrous Heme Iron in Deoxy Myoglobin Reconstituted with Trifluoromethyl Group-Substituted Heme Cofactors

Palmitate interaction with physiological states of myoglobin

Variation and Analysis of Second-Sphere Interactions and Axial Histidinate Character inc-type Cytochromes

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