Linear electric field effect measurements of variant low-spin forms of ferric cytochrome c

Mims, W. B.; Peisach, Jack

doi:10.1021/bi00713a026

Cited by 16 publications

(3 citation statements)

References 18 publications

(21 reference statements)

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“…At the heart of this work is the idea that the spin system at the active site of the protein is a unique physical system whose Zeeman interaction is describable by a Cartesian tensor. This physical system is stressed by an electric field (31) or mechanical force (22) that originates outside the protein. The relationship between the perturbing stress and the g tensor of the spin system is described by another (stress-strain) tensor.…”

Section: Discussionmentioning

confidence: 99%

“…On the other hand, the work of Hagen (12,18) has shown that changes in the freezing process can affect the EPR signal of many proteins. Freezing is also a process that can cause large local charge densities (41) and thereby change EPR spectra via electric fields (31). Therefore, if freezing is an important contribution to g strain, then separating mechanical strain from electric-field strain will be a very difficult problem.…”

Section: Discussionmentioning

confidence: 99%

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An analysis of g strain in the EPR of two [2Fe2S] ferredoxins. Evidence for a protein rigidity model

Hearshen¹,

Hagen

Sands

et al. 1986

Journal of Magnetic Resonance (1969)

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Replacing current notions of a pammagnetic center in a metalloprotein as a single entity in vivo with the more real&tic concept of an ensemble of spin systems, each uniquely dishded by its own surrounding protein leads to a rigorous description of the spectroscopic factor, g, as a random variable whose statistical properties contain information on the rigidity of the protein. Generation of a consistent set of accurate simulations of very lownoise, multifrequency (3,9,15 GHz) EPR data Corn selected S = 4 proteins has now been achieved. This consistency lends support to the physical and biological inferences drawn from such simulations. The spectml contribution of magnetic hyperfme line-broadening is minimized by studying the "Fe reconstituted [2Fe-2S] cluster in fully deuterated ferredoxin from Synechococcus lividus and the 'Hz0 exchanged [2Fe-2S] ferredoxin from Pseudomonas putida. High-resolution M&batter data on oxidixed and reduced "Fe reconstituted S. lividus ferredoxin are also presented. The oxidized spectrum shows that the inequivalence of the two ferric ions in a [2Fe-2S] cluster can be resolved as two Miissbauer lines. The complete absence of this splitting in the ferric lines of the reduced spectrum is definitive proof that the reducing electron always resides at the same Fe atom in frozen aqueous solutions. To explain the distributed nature of the paramagnetic site in the ferredoxins, three models are considered: (1) a multiplicity of EPR states; (2) external perturbations to the molecular Hamiltonian; (3) a distribution in the crystal field Hamiltonian parameters. The first model is discarded, the second is possible but difficult to verify, and the third model is shown to fit the data well. The latter comparison requires a correction to literature expressions for the g and A tensors in [2Fe-2S] clusters. Statistical analysis strongly suggests that the EPR of metalloproteins in its details is a reflection of protein structure that distributes its spatial coordinates, accommodating different levels of rigidity, the more flexible parts being located at the outside. Q 1986 Academic PBS, hc.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

An analysis of g strain in the EPR of two [2Fe2S] ferredoxins. Evidence for a protein rigidity model

Hearshen¹,

Hagen

Sands

et al. 1986

Journal of Magnetic Resonance (1969)

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“…The first eight additions of base were 5 µ each, the next three were 10 µeach, and the last addition was 5 µ\* of 80 mM base. Peisach, 1974). In all experiments, the concentration of heme was from 1 to 5 mM.…”

Section: [P][h20]mentioning

confidence: 99%

Linear electric field effect in electron paramagnetic resonance for two bisimidazole-heme complexes, model compounds for B and H hemichromes of hemoglobin and for cytochrome b₅

Peisach¹,

Mims²

1977

Biochemistry

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Bisimidazole-ferric heme is considered to be the structure at the heme site of cytochrome b5 and two different low spin ferric hemochromes spontaneously formed from ferric hemoglobin. The addition of strong base to bisimidazole-ferric heme in organic solvents alters the optical and magnetic properties of this compound. With the use of the linear electric field effect in the electron paramagnetic resonance, we demonstrate that addition of base does not lead to the exchange of hydroxide anion for ligated imidazole and that the bisimidazole structure is retained. Analysis of optical titrations indicates that 2 equiv of base react reversibly with bisimidazole-ferric heme. It is suggested that the two hemichromes formed from hemoglobin differ in structure from one another by the state of protonation of N-1 in the bound imidazoles.

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Biological Applications of Time Domain ESR

Thomann

Dalton

1984

Biological Magnetic Resonance

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Linear electric field effect measurements of variant low-spin forms of ferric cytochrome c

Cited by 16 publications

References 18 publications

An analysis of g strain in the EPR of two [2Fe2S] ferredoxins. Evidence for a protein rigidity model

An analysis of g strain in the EPR of two [2Fe2S] ferredoxins. Evidence for a protein rigidity model

Linear electric field effect in electron paramagnetic resonance for two bisimidazole-heme complexes, model compounds for B and H hemichromes of hemoglobin and for cytochrome b₅

Biological Applications of Time Domain ESR

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Linear electric field effect measurements of variant low-spin forms of ferric cytochrome c

Cited by 16 publications

References 18 publications

An analysis of g strain in the EPR of two [2Fe2S] ferredoxins. Evidence for a protein rigidity model

An analysis of g strain in the EPR of two [2Fe2S] ferredoxins. Evidence for a protein rigidity model

Linear electric field effect in electron paramagnetic resonance for two bisimidazole-heme complexes, model compounds for B and H hemichromes of hemoglobin and for cytochrome b5

Biological Applications of Time Domain ESR

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Linear electric field effect in electron paramagnetic resonance for two bisimidazole-heme complexes, model compounds for B and H hemichromes of hemoglobin and for cytochrome b₅