On the theory of the pseudocontact contribution to the N.M.R. shifts in paramagnetic systems

Golding, R.M.; Pascual, R.O.; Stubbs, L.C

doi:10.1080/00268977600101531

Cited by 22 publications

(6 citation statements)

References 6 publications

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“…Magnetic susceptibility tensor components as well as potential structural changes between redox states can be assessed from eq 2. It is, however, necessary to assume that the electronic density is localized at the iron center, a simplification that is only fully justified for nuclei located at more than 10 Å away from the metal center . This criterion is satisfied by all of the protein backbone nuclei considered here.…”

Section: Resultsmentioning

confidence: 99%

Magnetic Susceptibility Tensor and Heme Contact Shifts Determinations in the Rhodobacter capsulatus Ferricytochrome c‘: NMR and Magnetic Susceptibility Studies

et al. 2001

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The 1H and 15N resonances of the carbon monoxide complex of ferrocytochrome c' of Rhodobacter capsulatus, a ferrous diamagnetic heme protein, have been extensively assigned by TOCSY-HSQC, NOESY-HSQC, and HSQC-NOESY-HSQC 3D heteronuclear experiments performed on a 7 mM sample labeled with 15N. Based on short-range and medium-range NOEs and H(N) exchange rates, the secondary structure consists of four helices: helix 1 (3-29), helix 2 (33-48), helix 3 (78-101), and helix 4 (103-125). The 15N, 1HN, and 1H(alpha) chemical shifts of the CO complex form are compared to those of the previously assigned oxidized (or ferric) state. From the chemical shift differences between these redox states, the orientation and the anisotropy of the paramagnetic susceptibility tensor have been determined using the crystallographic coordinates of the ferric state. The chi-tensor is axial, and the orientation of the z-axis is approximately perpendicular to the heme plane. The paramagnetic chemical shifts of the protons of the heme ligand have been determined and decomposed into the Fermi shift and dipolar shift contributions. Magnetic susceptibility studies in frozen solutions have been performed. Fits of the susceptibility data using the model of Maltempo (Maltempo, M. M. J. Chem. Phys. 1974, 61, 2540-2547) are consistent with a rather low contribution of the S = 3/2 spin state over the range of temperatures and confirm the value of the axial anisotropy. Values in the range 10.4-12.5 cm(-1) have been inferred for the axial zero-field splitting parameter (D). Analysis of the contact shift and the susceptibility data suggests that cytochrome c' of Rb. capsulatus exhibits a predominant high-spin character of the iron in the oxidized state at room temperature.

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Section: Resultsmentioning

confidence: 99%

Magnetic Susceptibility Tensor and Heme Contact Shifts Determinations in the Rhodobacter capsulatus Ferricytochrome c‘: NMR and Magnetic Susceptibility Studies

et al. 2001

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“…Magnetic properties of the reduced state as well as potential structural differences between states can be assessed using eq 2. It is, however, necessary to assume that the electron density of the ferrous state is located at the Fe center, a simplification which is only justified for nuclei that are located at least 10 Å away from the metal center . This criterion is satisfied by all of the backbone nuclei considered in the present discussion.…”

Section: Resultsmentioning

confidence: 99%

Unusual Contact Shifts and Magnetic Tensor Orientation in Rhodobacter capsulatus Ferrocytochrome c‘: NMR, Magnetic Susceptibility, and EPR Studies

et al. 1999

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In contrast to high-spin ferrous paramagnetic heme proteins, the chemical shifts of the heme protons are very unusual in the ferrocytochromes c′. Magnetic susceptibility studies of Rhodobacter capsulatus ferrocytochrome c′ in frozen solutions have been performed and indicate an S ) 2 spin state and a large negative axial (D) zero-field splitting parameter (-18.3 cm -1 ) as well as a significant rhombic (E) value (-4.9 cm -1 ). The 1 H and 15 N resonances have been extensively assigned by TOCSY-HSQC, NOESY-HSQC, and HSQC-NOESY-HSQC 3-D heteronuclear experiments performed on a 8 mM sample labeled with 15 N. Based on short-range and medium-range NOEs and H N exchange rates, the secondary structure consists of four helices: helix-1 (3-30), helix-2 (34-49), helix-3 (78-97), and helix-4 (103-117). The 15 N, H N , and H R chemical shifts of the reduced (or ferro) state are compared to those previously assigned for the diamagnetic carbon monoxide complex form. From the chemical shift differences between these redox states, the orientation and the anisotropy of the paramagnetic susceptibility tensor have been determined using the crystallographic coordinates of the ferric state. Values of -23 and -3 cm -1 have been inferred for D and E, and the z-axis of the tensor is tilted approximately 30°from the normal to the heme. The paramagnetic chemical shifts of the heme protons have been determined and split up into Fermi shift and the dipolar shift contributions. The pattern of the contact shifts is very unusual, exhibiting a 2-fold symmetry, and is discussed in terms of molecular orbital interactions between the porphyrin macrocycle and the imidazole ring.

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“…Magnetic properties of the different spin states can be assessed using eq 3 by a fit of the magnetic susceptibility magnitude and orientation. For the paramagnetic states, it is, however, necessary to assume that the electron density is localized on the Fe center, a simplification which is only justified for nuclei located at least 10 Å away from the metal center . This criterion is justified for all the nuclei considered in the present discussion.…”

Section: Resultsmentioning

confidence: 99%

NMR Determination of the Magnetic Susceptibility Anisotropy of Cytochromec‘ ofRhodobacterCapsulatusby¹J_HNDipolar Coupling Constants Measurement: Characterization of Its Monomeric State in Solution

et al. 2000

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J NH splittings have been measured at 600 and 400 MHz on the paramagnetic (S ) 2 and S ) 5 / 2 ) and on the diamagnetic state (S ) 0) of cytochrome c′ of Rhodobacter capsulatus. Residual dipolar splittings and the magnetic susceptibility tensor have been then derived using two methods. The first method equaled for a paramagnetic species the dipolar splitting to the difference of the measured 1 J NH splittings between the paramagnetic and diamagnetic forms at one field. The second method consisted in deriving the total magnetic tensor of the paramagnetic forms from the splittings at two fields with a post-correction for the diamagnetic contribution. Both methods are shown to produce equivalent results for the determination of the susceptibility magnetic tensor. Comparison with the magnetic tensor obtained with a previous study based on the dipolar shifts leads to the evidence that, unlike most other cytochromes c′, Rb. capsulatus cytochrome c′ of strain M1131 is monomeric in solution. This result is discussed in view of the cytochrome c′ function. Our study confirms that dipolar splittings are a powerful tool for structure determination, providing insight not only into local structural details but also into the global fold of molecules.

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On the theory of the pseudocontact contribution to the N.M.R. shifts in paramagnetic systems

Cited by 22 publications

References 6 publications

Magnetic Susceptibility Tensor and Heme Contact Shifts Determinations in the Rhodobacter capsulatus Ferricytochrome c‘: NMR and Magnetic Susceptibility Studies

Magnetic Susceptibility Tensor and Heme Contact Shifts Determinations in the Rhodobacter capsulatus Ferricytochrome c‘: NMR and Magnetic Susceptibility Studies

Unusual Contact Shifts and Magnetic Tensor Orientation in Rhodobacter capsulatus Ferrocytochrome c‘: NMR, Magnetic Susceptibility, and EPR Studies

NMR Determination of the Magnetic Susceptibility Anisotropy of Cytochromec‘ ofRhodobacterCapsulatusby¹J_HNDipolar Coupling Constants Measurement: Characterization of Its Monomeric State in Solution

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On the theory of the pseudocontact contribution to the N.M.R. shifts in paramagnetic systems

Cited by 22 publications

References 6 publications

Magnetic Susceptibility Tensor and Heme Contact Shifts Determinations in the Rhodobacter capsulatus Ferricytochrome c‘: NMR and Magnetic Susceptibility Studies

Magnetic Susceptibility Tensor and Heme Contact Shifts Determinations in the Rhodobacter capsulatus Ferricytochrome c‘: NMR and Magnetic Susceptibility Studies

Unusual Contact Shifts and Magnetic Tensor Orientation in Rhodobacter capsulatus Ferrocytochrome c‘: NMR, Magnetic Susceptibility, and EPR Studies

NMR Determination of the Magnetic Susceptibility Anisotropy of Cytochromec‘ ofRhodobacterCapsulatusby1JHNDipolar Coupling Constants Measurement: Characterization of Its Monomeric State in Solution

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NMR Determination of the Magnetic Susceptibility Anisotropy of Cytochromec‘ ofRhodobacterCapsulatusby¹J_HNDipolar Coupling Constants Measurement: Characterization of Its Monomeric State in Solution