Interpretation of electron spin resonance spectra due to some B12-dependent enzyme reactions

Boas, John F.; Hicks, Peter R.; Pilbrow, John R.; Smith, Thomas D.

doi:10.1039/f29787400417

Cited by 73 publications

(109 citation statements)

References 2 publications

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“…This is perhaps mostly due to the tethering of the nitroxide side chain, provided that the backbone of the helix is fixed. When the interspin distance is very small, the EPR line shape may become complicated due to the short-range interactions such asJ coupling and the magnetic anisotropy (15,24). Despite several attempts to elucidate these matters, it is unclear how they affect the EPR line shape at very short distances in the frozen state.…”

Section: Discussionmentioning

confidence: 99%

“…It has been shown that this method accurately measures the interspin distance in the range of [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] A. The accurate determination of distances in this range may be crucial for the understanding of mechanisms of signal transduction or energy transduction involving subtle structural rearrangements (28,29).…”

Section: Discussionmentioning

confidence: 99%

“…The EPR absorption lines are then split by 2B in the magnetic field (12,14): 2B = ( C)ge,3cOS20o )/r3, [1] where ge is the isotropic g value of the electrons, f3 is the electron Bohr magneton (jg43 = 30.3 GA3), and 0 is the angle between the interspin vector and the external magnetic field. Here we assume that the effect of anisotropic magnetic tensors is negligible (15).…”

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confidence: 99%

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Determination of the distance between two spin labels attached to a macromolecule.

Rabenstein

Shin

1995

Proc. Natl. Acad. Sci. U.S.A.

398

450

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An EPR "spectroscopic ruler" was developed using a series of a-helical polypeptides, each modified with two nitroxide spin labels. The EPR line broadening due to electron-electron dipolar interactions in the frozen state was determined using the Fourier deconvolution method. These dipolar spectra were then used to estimate the distances between the two nitroxides separated by 8-25 A. Results agreed well with a simple a-helical model. The standard deviation from the model system was 0.9 A in the range of [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] A. This technique is applicable to complex systems such as membrane receptors and channels, which are difficult to access with high-resolution NMR or x-ray crystallography, and is expected to be particularly useful for systems for which optical methods are hampered by the presence of lightinterfering membranes or chromophores.Many studies in structural biology are dependent on the physical techniques to measure distances in proteins and nucleic acids. X-ray crystallography and high-resolution NMR have been useful in determining the three-dimensional structures of relatively simple biological macromolecules. For complex systems such as membrane proteins, fluorescence energy transfer (FET) has been the main alternative for measuring distances up to 80 A. FET has been successful for studies of intermolecular organization in biological systems (1, 2), ligandreceptor interactions (3), and structures of nucleic acids (4).Recently, site-directed spin labeling EPR has become useful for studying proteins (5, 6). One or two native residues are mutated to cysteines, which are then labeled with thiol-specific nitroxide spin labels. This technique can also be used to study local secondary structure (7,8). Nucleic acids also appear to be amenable to spin labeling (9). Although spin labeling has been used to estimate distances in the past (10-12), no EPR "spectroscopic ruler" similar to that developed by Stryer and Haugland (13) for FET has been constructed or tested on model systems.In this work a convenient and accurate EPR method to determine distances between two site-specifically placed nitroxides in the range of 8-25 A in biomacromolecules is presented. In this method the pure dipolar spectrum for two interacting spins in the frozen state is directly Fourier deconvoluted from the dipolar broadened continuous-wave EPR spectrum. The average interspin distance and the variance of its distribution are obtained from this dipolar spectrum.The method was tested using a-helical peptides as a model system. The peptides were alanine-based helices with spinlabeled cysteines substituted for alanines at two locations from 1 to 13 residues apart. There is excellent agreement between the spin-spin distances from a simple model and experimental results in the range of 8-25 A. It is also shown that this method is useful for systems that have impurities of singly labeled species. Although this methodology is complementary to FET, EPR has the advantages of easier...

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

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Determination of the distance between two spin labels attached to a macromolecule.

Rabenstein

Shin

1995

Proc. Natl. Acad. Sci. U.S.A.

398

450

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“…To facilitate visual comparison with the field-swept experimental spectra the values of J, A M , A N , and ANt are discussed below in units of G with the conversion between Hertz and Gauss given by eqs. [2]- [4]. The conversion factor for A N is the same as for A M .…”

Section: Computer Simulationsmentioning

confidence: 98%

“…This approach has been used by many investigators to obtain metrical information on spin-labeled biomolecules (1). Others have studied the closely related problem of metal -organic radical interactions in vitamin BI2-dependent enzyme reactions also seeking metrical information (4,5).…”

Section: Introductionmentioning

confidence: 99%

Metal-nitroxyl interactions. 25. Exchange interactions via saturated linkages in spin-labeled porphyrins

More¹,

Eaton²

1982

Can. J. Chem.

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A series of spin-labeled copper porphyrins has been prepared in which nitroxyl radicals are attached toa porphyrin pyrrole ring by propionamide and propionate ester linkages. The solution epr spectra at room temperature indicate that the values of the electron ..spin-electron spin-coipling constant, J , for these compounds are in the range 4 to 18 G, dependingon the solvent and the size of the nitroxyl ring. Below -45°C two isomers with different values of J were observed in the epr spectra of two of the compounds. Variable temperature epr spectra were also analyzed for analogous spin-labeled copper porphyrins which have cis and trans acrylic ester and acrylamide linkages between the porphyrin and the nitroxyl ring.

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Magnetic field effects on coenzyme B12-dependent enzymes: Validation of ethanolamine ammonia lyase results and extension to human methylmalonyl CoA mutase

Taoka

Padmakumar

Grissom

et al. 1997

Bioelectromagnetics

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Enzymes with radical‐pair intermediates have been considered as a likely target for purported magnetic field effects in humans. The bacterial enzyme ethanolamine ammonia lyase and the human enzyme methylmalonyl‐CoA mutase catalyze coenzyme B12‐dependent rearrangement reactions. A common step in the mechanism of these two enzymes is postulated to be homolysis of the cobalt‐carbon bond of the cofactor to generate a spin‐correlated radical pair consisting of the 5′‐deoxyadenosyl radical and cob(II)alamin [Ado· Cbl(II)]. Thus, the reactions catalyzed by these enzymes are expected to be sensitive to an applied magnetic field according to the same principles that control radical pair chemical reactions. The magnetic field effect on ethanolamine ammonia lyase reported previously has been corroborated independently in one of the authors' laboratory. However, neither the human nor the bacterial mutase from Propionibacterium shermanii exhibits a magnetic field effect that could be greater than about 15%, considering the error limit imposed by the uncertainty of the coupled assay. Our studies suggest that putative magnetic field effects on physiological processes are not likely to be mediated by methylmalonyl‐CoA mutase. Bioelectromagnetics 18:506–513, 1997. © 1997 Wiley‐Liss, Inc.

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Interpretation of electron spin resonance spectra due to some B12-dependent enzyme reactions

Cited by 73 publications

References 2 publications

Determination of the distance between two spin labels attached to a macromolecule.

Determination of the distance between two spin labels attached to a macromolecule.

Metal-nitroxyl interactions. 25. Exchange interactions via saturated linkages in spin-labeled porphyrins

Magnetic field effects on coenzyme B12-dependent enzymes: Validation of ethanolamine ammonia lyase results and extension to human methylmalonyl CoA mutase

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