ISSN:
1432-1327
Keywords:
Mercury-substituted rubredoxin
;
Mercury-thiolate charge-transfer bands
;
Cysteine ligation
;
Electronic spectroscopy
;
Perturbed angular correlation of γ-rays spectroscopy
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
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.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/PL00010668
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