Electron nuclear double resonance on heme compounds. ENDOR from the iron ligands in protohemin chloride and protohemin bromide

Camp, H. L. Van; Scholes, Charles P.; Mulks, C. F.

doi:10.1021/ja00430a014

Cited by 19 publications

(15 citation statements)

References 1 publication

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“…The nuclear quadrupole coupling is not resolved but, according to the width of the lines the nuclear quadrupolar coupling constant (Q z ), is smaller than 0.4 MHz. The parameters for this nucleus are close to those reported for the heme nitrogens in other HS centers (40)(41)(42)(43). In Fig.…”

Section: Endor and Hyscoresupporting

confidence: 87%

“…Changes in the hyperfine coupling parameters of nuclei in the porphyrin plane have been observed by NMR and related to the coordination number in ferric HS hemoproteins (52). Moreover, the variation of heme nitrogen couplings on changes in heme axial coordination has been studied in a series of ENDOR experiments, and the authors have concluded that the larger couplings could be correlated to a five-coordinated heme, whereas smaller couplings would be associated with the six-coordinated hemin (42,43). All of this experimental evidence indicates, then, that CcmE is fivecoordinated, in agreement with the structural model ( 5) that proposes the heme docked on the hydrophobic platform formed by the residues Phe 37 , Val 110 , and Leu 127 .…”

Section: Discussionmentioning

confidence: 99%

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Axial Coordination of Heme in Ferric CcmE Chaperone Characterized by EPR Spectroscopy

García-Rubio

Braun

Gromov

et al. 2007

Biophysical Journal

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In Escherichia coli cytochrome c maturation requires a set of eight proteins including the heme chaperone CcmE, which binds heme transiently, yet covalently. Several variants of CcmE were purified and analyzed by continuous-wave electron paramagnetic resonance, electron nuclear double resonance, and hyperfine sublevel correlation spectroscopy to investigate the heme axial coordination. Results reveal the presence of a number of coordination environments, two high-spin heme centers with different rhombicities, and at least one low-spin heme center. The low-spin species was shown to be an artifact induced by the presence of available histidines in the vicinity of the iron. Both of the high-spin forms are five-coordinated, and comparison of the spectra of the wild-type CcmE with those of the mutant CcmE(Y134H) proves that the higher-rhombicity form is coordinated by Tyr134. The low-rhombicity (axial) form does not have a histidine residue or a water molecule as an axial ligand. However, we identified exchangeable protons coupled to the iron ion. We propose that the axial form can be coordinated by a carboxyl group of an acidic residue in the flexible domain of the protein. The two species would represent two different conformations of the flexible alpha-helix domain surrounding the heme. This conformational flexibility confers CcmE special dynamic properties that are certainly important for its function.

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Section: Endor and Hyscoresupporting

confidence: 87%

Section: Discussionmentioning

confidence: 99%

Axial Coordination of Heme in Ferric CcmE Chaperone Characterized by EPR Spectroscopy

García-Rubio

Braun

Gromov

et al. 2007

Biophysical Journal

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“…One of the several functional states of heme proteins involves a ferric heme iron, Fe 3+ (d 5 ), in a high-spin (HS) configuration, S ) 5/2. Because of the paramagnetic nature of this state, electron paramagnetic resonance (EPR) techniques provide excellent characterization tools for this system.…”

Section: Introductionmentioning

confidence: 99%

“…ENDOR has yielded very detailed information about the directly coordinated nitrogens of the porphyrin ring in HS heme proteins, [3][4][5][6][7] but in most cases, the full set of magnetic parameters could only be derived from single-crystal EN-DOR studies. 5 Information on the hyperfine interactions of the more remote nuclei is generally obtained from NMR studies.…”

Section: Introductionmentioning

confidence: 99%

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A Multifrequency HYSCORE Study of Weakly Coupled Nuclei in Frozen Solutions of High-Spin Aquometmyoglobin

et al. 2008

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In this work, we show the extreme power of multifrequency HYSCORE (hyperfine sublevel correlation spectroscopy) techniques to unravel the hyperfine interactions of the electron spin with the remote nuclei in the heme site of high-spin ferric heme proteins. Horse heart aquo-metmyoglobin was used as a model system to demonstrate the power of these techniques. Experimental evidence was collected and assigned to protons of the proximal histidine ligand, to the mesoprotons of the heme ligand, and to two different protons of the distal water ligand. The latter difference relates to the stabilization of the water ligand by the E7His residue. Furthermore, HYSCORE signals of the remote N(delta) of the proximal (F8) and N(epsilon) of the distal (E7) histidine were detected. Finally, correlation peaks from the lesser-abundant (13)C nuclei of the heme ligand could be detected. These novel results allow dissection of the hyperfine couplings into individual contributions and calculation of the spin density in the pi and sigma orbitals, thus completing earlier electron paramagnetic resonance and liquid-state NMR data.

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Iron 10‐Thiacorroles: Bioinspired Iron(III) Complexes with an Intermediate Spin (S=3/2) Ground State

Sakow

Baabe

Böker

et al. 2014

Chemistry A European J

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A first systematic study upon the preparation and exploration of a series of iron 10-thiacorroles with simple halogenido (F, Cl, Br, I), pseudo-halogenido (N3 , I3 ) and solvent-derived axial ligands (DMSO, pyridine) is reported. The compounds were prepared from the free-base octaethyl-10-thiacorrole by iron insertion and subsequent ligand-exchange reactions. The small N4 cavity of the ring-contracted porphyrinoid results in an intermediate spin (i.s., S=3/2) state as the ground state for the iron(III) ion. In most of the investigated cases, the i.s. state is found unperturbed and independent of temperature, as determined by a combination of X-ray crystallography and magnetometry with (1) H NMR-, EPR-, and Mössbauer spectroscopy. Two exceptions were found. The fluorido iron(III) complex is inhomogenous in the solid and contains a thermal i.s. (S=3/2)→high spin (h.s., S=5/2) crossover fraction. On the other side, the cationic bis(pyridine) complex resides in the expected low spin (l.s., S=1/2) state. Chemically, the iron 10-thiacorroles differ from the iron porphyrins mainly by weaker axial ligand binding and by a cathodic shift of the redox potentials. These features make the 10-thiacorroles interesting ligands for future research on biomimetic catalysts and model systems for unusual heme protein active sites.

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Electron nuclear double resonance on heme compounds. ENDOR from the iron ligands in protohemin chloride and protohemin bromide

Cited by 19 publications

References 1 publication

Axial Coordination of Heme in Ferric CcmE Chaperone Characterized by EPR Spectroscopy

Axial Coordination of Heme in Ferric CcmE Chaperone Characterized by EPR Spectroscopy

A Multifrequency HYSCORE Study of Weakly Coupled Nuclei in Frozen Solutions of High-Spin Aquometmyoglobin

Iron 10‐Thiacorroles: Bioinspired Iron(III) Complexes with an Intermediate Spin (S=3/2) Ground State

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