ISSN:
1432-1327
Keywords:
Key words Electron nuclear double resonance
;
Ferredoxin
;
Arthrospira platensis
;
g-Tensor
;
Spin population
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Abstract The 1H electron nuclear double resonance (ENDOR) spectra in frozen solutions of the reduced [2Fe-2S] cluster in ferredoxin from Arthrospira (Spirulina) platensis have been measured at low temperatures (5–20 K) and simulated using orientational selection methods. The analysis confirmed the existence of a single paramagnetic species with iron valence states II and III connected uniquely to the cluster irons. The experimental ENDOR spectra were fitted to a model including the spin distribution on the centre, the orientation of the g-matrix, and the isotropic and anisotropic hyperfine couplings of the nearest protons in the crystallographically determined structure. In order to partially simulate ENDOR line shapes, a statistical distribution of the corresponding torsion angles between the Fe(III) centre and one of the β-CH2 protons was introduced. From the analysis, four of the larger hyperfine couplings found were assigned to the cysteine β-protons near the Fe(III) ion of the cluster, with isotropic hyperfine couplings ranging from 1.6 to 4.1 MHz. The spin distribution on the two iron ions was estimated to be +1.85 for the Fe(III) ion and −0.9 for the Fe(II) ion. The Fe(III) ion was identified as being coordinated to the cysteine ligands Cys49 and Cys79, confirming previous NMR results. The direction of the g-tensor with respect to the cluster was deduced. The g 1-g 2 plane is parallel to the planes through each iron and its adjacent cysteine sulfurs; the g 2-g 3 plane is nearly perpendicular to the latter planes and deviates by 25° from the FeSSFe plane. The g 1 direction is dominated by the bonding geometry of Fe(II) and does not align with the Fe(II)-Fe(III) vector.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s007750050012
Permalink
