Electronic Structure of Low-Spin Ferric Porphyrins: 13C NMR Studies of the Influence of Axial Ligand Orientation
Autor(a) principal: | |
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Data de Publicação: | 1998 |
Outros Autores: | , , , , |
Tipo de documento: | Artigo |
Idioma: | eng |
Título da fonte: | Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos) |
Texto Completo: | http://hdl.handle.net/10400.6/4616 |
Resumo: | Heteronuclear multiple quantum NMR is used to measure the paramagnetic 13C shifts of the α substituents of the hemes in five different tetraheme ferricytochromes c3. The shifts of the 20 bis-histidine ligated hemes are assigned and then analyzed in terms of a model based on the π molecular orbitals of the heme under perturbed D4 symmetry, which yields the orientation of the rhombic perturbation, θ, and an energy splitting parameter, ΔE. Comparison of these parameters with crystal structures provides a test of the nature and extent of the influence of axial ligand orientation on the electronic structure of the heme. Despite possible differences between structures in solution and in the crystal, a clear correlation is found between θ and the resultant of the normals to the imidazole planes, and between ΔE and the angle between the normals. A weaker dependence of ΔE upon θ is also apparent. This is analogous to the results of low-temperature EPR studies of model compounds, which have been attributed to pseudo-Jahn−Teller distortion of the porphyrin. However, the effect is also predicted by extended Hückel calculations made with undistorted geometries. This work demonstrates that the variation in the electronic structure of bis-histidinyl hemes c is dominated by the geometry of the axial ligands and that other perturbations, such as asymmetric substitution of the porphyrin or low symmetry of the surrounding protein, are relatively minor. The correlations with θ and ΔE can, therefore, be used to determine the ligand geometry with sufficient accuracy to detect differences between structures in solution and in the crystal. The analysis can also be used to locate the principal axes of the magnetic susceptibility tensors of ferrihemes as well as providing orientational constraints for the axial ligands for the calculation of solution structures of paramagnetic proteins. This is particularly important since paramagnetic relaxation may make it impossible to observe NOE effects to the imidazole protons, leaving the geometry of the heme pocket poorly defined. |
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Electronic Structure of Low-Spin Ferric Porphyrins: 13C NMR Studies of the Influence of Axial Ligand OrientationNMRHeme ProteinsElectronic StructureHeteronuclear multiple quantum NMR is used to measure the paramagnetic 13C shifts of the α substituents of the hemes in five different tetraheme ferricytochromes c3. The shifts of the 20 bis-histidine ligated hemes are assigned and then analyzed in terms of a model based on the π molecular orbitals of the heme under perturbed D4 symmetry, which yields the orientation of the rhombic perturbation, θ, and an energy splitting parameter, ΔE. Comparison of these parameters with crystal structures provides a test of the nature and extent of the influence of axial ligand orientation on the electronic structure of the heme. Despite possible differences between structures in solution and in the crystal, a clear correlation is found between θ and the resultant of the normals to the imidazole planes, and between ΔE and the angle between the normals. A weaker dependence of ΔE upon θ is also apparent. This is analogous to the results of low-temperature EPR studies of model compounds, which have been attributed to pseudo-Jahn−Teller distortion of the porphyrin. However, the effect is also predicted by extended Hückel calculations made with undistorted geometries. This work demonstrates that the variation in the electronic structure of bis-histidinyl hemes c is dominated by the geometry of the axial ligands and that other perturbations, such as asymmetric substitution of the porphyrin or low symmetry of the surrounding protein, are relatively minor. The correlations with θ and ΔE can, therefore, be used to determine the ligand geometry with sufficient accuracy to detect differences between structures in solution and in the crystal. The analysis can also be used to locate the principal axes of the magnetic susceptibility tensors of ferrihemes as well as providing orientational constraints for the axial ligands for the calculation of solution structures of paramagnetic proteins. This is particularly important since paramagnetic relaxation may make it impossible to observe NOE effects to the imidazole protons, leaving the geometry of the heme pocket poorly defined.he authors are grateful to Professor J. LeGall for kindly providing the protein samples. This work was supported by PRAXIS XXI (BD 2509/93), PRAXIS/PCN/BIO/ 0074/96, and EC contract No. ERBFMRXCT980218.ACS PublicationsuBibliorumLouro, RicardoCorreia, I. J.Brennan, LorraineCoutinho, IsabelXavier, AntónioTurner, David2018-03-14T17:25:31Z1998-12-041998-12-04T00:00:00Zinfo:eu-repo/semantics/publishedVersioninfo:eu-repo/semantics/articleapplication/pdfhttp://hdl.handle.net/10400.6/4616engLouro, R.O., Correia, I.J., Brennan, L., Coutinho, I.B., Xavier, A.V. e Turner, D.L. (1998) “Electronic structure of low-spin ferric porphyrins: 13C NMR studies of the influence of axial ligand orientation”, Journal of the American Chemical Society, Vol. 120(50), pp. 13240-1324710.1021/ja983102mmetadata only accessinfo:eu-repo/semantics/openAccessreponame:Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)instname:Agência para a Sociedade do Conhecimento (UMIC) - FCT - Sociedade da Informaçãoinstacron:RCAAP2023-12-15T09:41:41Zoai:ubibliorum.ubi.pt:10400.6/4616Portal AgregadorONGhttps://www.rcaap.pt/oai/openaireopendoar:71602024-03-20T00:45:40.809410Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos) - Agência para a Sociedade do Conhecimento (UMIC) - FCT - Sociedade da Informaçãofalse |
dc.title.none.fl_str_mv |
Electronic Structure of Low-Spin Ferric Porphyrins: 13C NMR Studies of the Influence of Axial Ligand Orientation |
title |
Electronic Structure of Low-Spin Ferric Porphyrins: 13C NMR Studies of the Influence of Axial Ligand Orientation |
spellingShingle |
Electronic Structure of Low-Spin Ferric Porphyrins: 13C NMR Studies of the Influence of Axial Ligand Orientation Louro, Ricardo NMR Heme Proteins Electronic Structure |
title_short |
Electronic Structure of Low-Spin Ferric Porphyrins: 13C NMR Studies of the Influence of Axial Ligand Orientation |
title_full |
Electronic Structure of Low-Spin Ferric Porphyrins: 13C NMR Studies of the Influence of Axial Ligand Orientation |
title_fullStr |
Electronic Structure of Low-Spin Ferric Porphyrins: 13C NMR Studies of the Influence of Axial Ligand Orientation |
title_full_unstemmed |
Electronic Structure of Low-Spin Ferric Porphyrins: 13C NMR Studies of the Influence of Axial Ligand Orientation |
title_sort |
Electronic Structure of Low-Spin Ferric Porphyrins: 13C NMR Studies of the Influence of Axial Ligand Orientation |
author |
Louro, Ricardo |
author_facet |
Louro, Ricardo Correia, I. J. Brennan, Lorraine Coutinho, Isabel Xavier, António Turner, David |
author_role |
author |
author2 |
Correia, I. J. Brennan, Lorraine Coutinho, Isabel Xavier, António Turner, David |
author2_role |
author author author author author |
dc.contributor.none.fl_str_mv |
uBibliorum |
dc.contributor.author.fl_str_mv |
Louro, Ricardo Correia, I. J. Brennan, Lorraine Coutinho, Isabel Xavier, António Turner, David |
dc.subject.por.fl_str_mv |
NMR Heme Proteins Electronic Structure |
topic |
NMR Heme Proteins Electronic Structure |
description |
Heteronuclear multiple quantum NMR is used to measure the paramagnetic 13C shifts of the α substituents of the hemes in five different tetraheme ferricytochromes c3. The shifts of the 20 bis-histidine ligated hemes are assigned and then analyzed in terms of a model based on the π molecular orbitals of the heme under perturbed D4 symmetry, which yields the orientation of the rhombic perturbation, θ, and an energy splitting parameter, ΔE. Comparison of these parameters with crystal structures provides a test of the nature and extent of the influence of axial ligand orientation on the electronic structure of the heme. Despite possible differences between structures in solution and in the crystal, a clear correlation is found between θ and the resultant of the normals to the imidazole planes, and between ΔE and the angle between the normals. A weaker dependence of ΔE upon θ is also apparent. This is analogous to the results of low-temperature EPR studies of model compounds, which have been attributed to pseudo-Jahn−Teller distortion of the porphyrin. However, the effect is also predicted by extended Hückel calculations made with undistorted geometries. This work demonstrates that the variation in the electronic structure of bis-histidinyl hemes c is dominated by the geometry of the axial ligands and that other perturbations, such as asymmetric substitution of the porphyrin or low symmetry of the surrounding protein, are relatively minor. The correlations with θ and ΔE can, therefore, be used to determine the ligand geometry with sufficient accuracy to detect differences between structures in solution and in the crystal. The analysis can also be used to locate the principal axes of the magnetic susceptibility tensors of ferrihemes as well as providing orientational constraints for the axial ligands for the calculation of solution structures of paramagnetic proteins. This is particularly important since paramagnetic relaxation may make it impossible to observe NOE effects to the imidazole protons, leaving the geometry of the heme pocket poorly defined. |
publishDate |
1998 |
dc.date.none.fl_str_mv |
1998-12-04 1998-12-04T00:00:00Z 2018-03-14T17:25:31Z |
dc.type.status.fl_str_mv |
info:eu-repo/semantics/publishedVersion |
dc.type.driver.fl_str_mv |
info:eu-repo/semantics/article |
format |
article |
status_str |
publishedVersion |
dc.identifier.uri.fl_str_mv |
http://hdl.handle.net/10400.6/4616 |
url |
http://hdl.handle.net/10400.6/4616 |
dc.language.iso.fl_str_mv |
eng |
language |
eng |
dc.relation.none.fl_str_mv |
Louro, R.O., Correia, I.J., Brennan, L., Coutinho, I.B., Xavier, A.V. e Turner, D.L. (1998) “Electronic structure of low-spin ferric porphyrins: 13C NMR studies of the influence of axial ligand orientation”, Journal of the American Chemical Society, Vol. 120(50), pp. 13240-13247 10.1021/ja983102m |
dc.rights.driver.fl_str_mv |
metadata only access info:eu-repo/semantics/openAccess |
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metadata only access |
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openAccess |
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application/pdf |
dc.publisher.none.fl_str_mv |
ACS Publications |
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ACS Publications |
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Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos) |
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Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos) |
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