ISSN:
1432-1327
Schlagwort(e):
Mercury-substituted rubredoxin
;
Mercury-thiolate charge-transfer bands
;
Cysteine ligation
;
Electronic spectroscopy
;
Perturbed angular correlation of γ-rays spectroscopy
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Biologie
,
Chemie und Pharmazie
Notizen:
Desulfovibrio gigas has been studied by electronic absorption, circular dichroism (CD), magnetic circular dichroism (MCD), and time differential perturbed angular correlation of γ-rays (TDPAC) spectroscopies. The TDPAC spectrum of 199mHg-Rd at pH 8 exhibits a prevailing nuclear quadrupole interaction (NQI) with a precession frequency of ω 1=0.09 Grad/s and an asymmetry parameter η=0, features characteristic of a slightly distorted tetrahedral tetrathiolate metal coordination, i.e, a HgCysS4 center. In addition, three minor populated NQIs have also been detected. They may represent a trigonal HgS3 (ω 1=1.13 Grad/s, η=0.21), a digonal HgS2 (ω 1= 1.34 Grad/s, η=0.20), and a digonal Hg(II) coordination (ω 1=1.58 Grad/s, η=0.18) with unidentified ligands. Since similar studies at pH 2.5 revealed a time-dependent increase of the HgCysS4 population, the low populated sites may represent intermediate Hg(II) complexes formed prior to the generation of the thermodynamically stable structure. The metal-induced absorption envelope of Hg-Rd reveals three distinct transitions with Gaussian-resolved maxima located at 230, 257, and 284 nm, which are paralleled by dichroic features in the corresponding difference CD spectrum of Hg(II)-Rd versus apo-Rd. Based on the optical electronegativity theory of Jørgensen, the lowest energy transition has been attributed to a CysS-Hg(II) charge-transfer excitation. The T d type of metal coordination in Hg-Rd is supported by the presence of an unresolved A-term with a negative lobe at 295 nm in the difference MCD spectrum. These results point to the usefulness of optical and TDPAC spectroscopies for studying Hg(II) sites in other proteins.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1007/PL00010668
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