ISSN:
1432-1017
Keywords:
Cytochrome b5
;
13C NMR
;
Fermi contact shift
;
Heme electronic structure
;
Ligand orientation
;
Heme rotation
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Physics
Notes:
Abstract Recently published chemical shifts for haem 13C nuclei in bovine ferricytochrome b 55 (Lee KB, Kweon J, Park H (1995) Assignment of hyperfine-shifted heme carbon resonances in ferricytochrome b 5. FEBS Lett. 367:77–80) are analysed in terms of haem molecular orbitals with perturbed D4h symmetry. Since a crystal structure of this protein is available, together with extensive 1H assignments both in the oxidised and reduced forms, the paramagnetic shifts can be separated into dipolar and Fermi contact contributions by using an empirical magnetic susceptibility tensor. The results are compared with the orientation of the tensor and the geometry of the haem ligands. This comparison casts doubt on one of the 13C assignments and demonstrates that the asymmetry of the haem electronic structure is dominated by the influence of both of the His ligands. The 13C chemical shifts of two haem methyl groups in the minor form of the protein, in which the haem is approximately rotated by 180° about its 5CH15CH axis, are also evaluated.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00180375
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