Coordination structure and chemical reactivity of hemoprotein-butyl peroxide complex

Jinno, Junichi; Shigematsu, Masayuki; Tajima, Kunihiko; Sakuraï, H.; Ohya-Nishiguchi, Hiroaki; Ishizu, Kazuhiko

doi:10.1016/s0006-291x(05)80237-2

Cited by 8 publications

(8 citation statements)

References 19 publications

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“…By comparing the EPR spectra of a number of samples, it was, however, possible to suggest that bands in the region of g ) 2.3 and g ) 2.2 are associated with the g ) 1.94 band. Taken together, these three lines correspond to a heme-peroxylike complex (Jino et al, 1991). The EPR spectral characteristics of this complex are similar to some of the intermediate states found in peroxidases (Coulson et al, 1971) and cytochrome P-450 (Tyson et al, 1972).…”

Section: Discussionsupporting

confidence: 64%

Production of Superoxide from Hemoglobin-Bound Oxygen Under Hypoxic Conditions

et al. 1996

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By low temperature electron paramagnetic resonance we have detected the formation of a free radical signal during incubation of partially oxygenated hemoglobin at 235 K. The observed signal has g parallel = 2.0565 and g perpendicular = 2.0043, consistent with the previously reported values for superoxide. The presence of additional EPR signals for oxygen-17 bound hemoglobin, with (017-017)A perpendicular = 63 G and (017-016)A perpendicular = 94 G under identical conditions, confirms the presence of a radical containing two nonequivalent oxygens as required for a superoxide in magnetically inequivalent environments. The superoxide radical has not previously been directly detected during hemoglobin autoxidation because of its rapid dismutation. Our ability to follow the formation of superoxide for more than 15 min is attributed to its production in the hydrophobic heme pocket where dismutation is slow. The enhanced production of this free radical at intermediate oxygen pressures is shown to coincide with enhanced rates of hemoglobin autoxidation for partially oxygenated intermediates. The formation of superoxide in the heme pocket under these conditions is attributed to enhanced heme pocket flexibility. Greater flexibility facilitates distal histidine interactions which destabilize the iron-oxygen bond resulting in the release of superoxide radical into the heme pocket.

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Section: Discussionsupporting

confidence: 64%

Production of Superoxide from Hemoglobin-Bound Oxygen Under Hypoxic Conditions

et al. 1996

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“…An electron transfer reaction involving the superoxide is confirmed by the detection (Figure 7) of a resonance at g ) 1.94. Such a signal is observed in other hemoproteins and iron complexes and is generally associated with g 3 of a lowspin Fe(III) heme peroxy complex (24), which is produced as a result of the one-electron reduction of superoxide.…”

Section: Discussionmentioning

confidence: 89%

“…The reaction of superoxide with an SH group to produce a thiyl radical would produce a peroxide in the heme pocket. Low-spin Fe(III) peroxy complexes (24) display rhombic EPR spectra and frequently have a g 3 of slightly less than 2. To determine whether such a signal is formed, it was necessary to improve the resolution in this region of the spectrum.…”

Section: Electron Paramagnetic Resonance Studies On Nonmodifiedmentioning

confidence: 99%

Superoxide Produced in the Heme Pocket of the β-Chain of Hemoglobin Reacts with the β-93 Cysteine To Produce a Thiyl Radical

et al. 1998

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The role of the beta-93 cysteine residue in the hemoglobin autoxidation process has been delineated by electron paramagnetic resonance. At low temperatures (8 K) after incubation at 235 K, free radical signals were detected. An analysis of the free radical spectrum produced implies that, besides the superoxide radical expected to be formed during autoxidation, an isotropic free radical is produced with a giso of 2.0133. This g value is consistent with that expected for a sulfur radical. Blocking the beta-93 sulfhydryl group with N-ethylmaleimide was found to eliminate the formation of the isotropic radical, but not the superoxide. This finding confirms the assignment of the isotropic radical as a thiyl radical originating from the oxidation of the cysteine SH group. A kinetic analysis of the time course for the formation of both the superoxide and thiyl radicals is consistent with a reversible electron transfer process between superoxide in the heme pocket of the beta-chains and the cysteine residue. This reaction is expected to produce both a thiyl radical and a peroxide. Direct evidence for peroxide production comes from the detection of a transient Fe(III) heme peroxide complex. The significance of the electron transfer process producing a thiyl radical is discussed. It is shown that the formation of the thiyl radical decreases the rate of autoxidation for the beta-chain and reduces heme degradation attributed to the reaction of superoxide with the heme. The insights gained from these low-temperature studies are believed to be relevant to room-temperature autoxidation.

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“…Synthesis of Alkyl Peroxide Porphyrinate Complexes. Alkyl peroxide complexes of TPPFe were synthesized by a modification of the synthetic procedures reported by Tajima and co-workers. − These investigators reported the synthesis and characterization (EPR and electronic absorption spectra) of [FeTPP(OCH 3 ) 2 ] - , [TPPFe(OCH 3 )(OO t Bu)] - , and [TPPFe(OO t Bu) 2 ] - in frozen glasses at 77 K. An important aim of the investigations reported here is the study of these complexes by 13 C NMR spectroscopy in solution. Consequently, modifications were necessary to synthesize and characterize the complexes at temperatures above the melting point of CH 2 Cl 2 .…”

Section: Methodsmentioning

confidence: 99%

“…Some years ago Tajima and co-workers showed that synthetic hemes in the presence of alkyl peroxides and a variety of sixth ligands, including methoxide, − imidazolate, or a second alkyl peroxide, as well as heme proteins with histidine , or cysteinate sixth ligands, yield very similar EPR spectra with compressed g anisotropy (∑ g 2 ≈ 14). These spectra are very similar to those obtained for the Fe III -OOH complexes of various heme protein enzymes, which were prepared by cryoreduction and then annealing of the corresponding Fe II -O 2 complexes. , The g -values of the complexes of Tajima and co-workers (2.32, 2.16, 1.95, methoxide, tert -butylperoxide; 2.25, 2.15, 1.96, bis- tert -butyl-peroxide; 2.32, 2.19, 1.94, imidazolate, hydroperoxide 20 ) are very similar to those of annealed hemoglobin-hydroperoxide (2.31, 2.18, 1.94), heme oxygenase-hydroperoxide (2.37, 2.19, 1.93), and cytochrome P450-hydroperoxide (2.29, 2.16, 1.96) .…”

Section: Introductionmentioning

confidence: 99%

Models of the Low-Spin Iron(III) Hydroperoxide Intermediate of Heme Oxygenase: Magnetic Resonance Evidence for Thermodynamic Stabilization of the d_x_y Electronic State at Ambient Temperatures

et al. 2002

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The (13)C pulsed ENDOR and NMR study of [meso-(13)C-TPPFe(OCH(3))(OO(t)Bu)](-) performed in this work shows that although the unpaired electron in low-spin ferrihemes containing a ROO(-) ligand resides in a d(pi) orbital at 8 K, the d(xy) electron configuration is favored at physiological temperatures. The variable temperature NMR spectra indicate a dynamic situation in which a heme with a d(pi) electron configuration and planar porphyrinate ring is in equilibrium with a d(xy) electron configuration that has a ruffled porphyrin ring. Because of the similarity in the EPR spectra of the hydroperoxide complexes of heme oxygenase, cytochrome P450, and the model heme complex reported herein, it is possible that these two electron configurations and ring conformations may also exist in equilibrium in the enzymatic systems. The ruffled porphyrinate ring would aid the attack of the terminal oxygen of the hydroperoxide intermediate of heme oxygenase (HO) on the meso-carbon, and the large spin density at the meso-carbons of a d(xy) electron configuration heme suggests the possibility of a radical mechanism for HO. The dynamic equilibrium between the ruffled (d(xy)) and planar (d(pi)) conformers observed in the model complexes also suggests that a flexible heme binding cavity may be an important structural motif for heme oxygenase activity.

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Coordination structure and chemical reactivity of hemoprotein-butyl peroxide complex

Cited by 8 publications

References 19 publications

Production of Superoxide from Hemoglobin-Bound Oxygen Under Hypoxic Conditions

Production of Superoxide from Hemoglobin-Bound Oxygen Under Hypoxic Conditions

Superoxide Produced in the Heme Pocket of the β-Chain of Hemoglobin Reacts with the β-93 Cysteine To Produce a Thiyl Radical

Models of the Low-Spin Iron(III) Hydroperoxide Intermediate of Heme Oxygenase: Magnetic Resonance Evidence for Thermodynamic Stabilization of the d_x_y Electronic State at Ambient Temperatures

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Coordination structure and chemical reactivity of hemoprotein-butyl peroxide complex

Cited by 8 publications

References 19 publications

Production of Superoxide from Hemoglobin-Bound Oxygen Under Hypoxic Conditions

Production of Superoxide from Hemoglobin-Bound Oxygen Under Hypoxic Conditions

Superoxide Produced in the Heme Pocket of the β-Chain of Hemoglobin Reacts with the β-93 Cysteine To Produce a Thiyl Radical

Models of the Low-Spin Iron(III) Hydroperoxide Intermediate of Heme Oxygenase: Magnetic Resonance Evidence for Thermodynamic Stabilization of the dxy Electronic State at Ambient Temperatures

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Models of the Low-Spin Iron(III) Hydroperoxide Intermediate of Heme Oxygenase: Magnetic Resonance Evidence for Thermodynamic Stabilization of the d_x_y Electronic State at Ambient Temperatures