COMPARATIVE NUCLEAR MAGNETIC-RESONANCE STUDIES OF HIGH-POTENTIAL IRON-SULFUR PROTEINS FROM CHROMATIUM-VINOSUM AND RHODOPSEUDOMONAS-GELATINOSA - ADDITIONAL HYPERFINE SHIFTED RESONANCES AND PH-DEPENDENT STRUCTURAL PERTURBATIONS

  • 1 January 1983
    • journal article
    • research article
    • Vol. 258  (13) , 8235-8239
Abstract
Proton NMR spectra and their dependence on pH are reproted for the oxidized and reduced forms of the high potential Fe-S proteins from C. vinosum and R. gelatinosa. Spectra of the protein from both species are very similar in the regions occupied by the hyperfine shifted resonances of protons located near the (Fe4S4(S-Cys)4) cluster. The oxidized protiens exhibit 3 new resonances that were not previously detected, 1 at very low field (about 100 ppm) and 2 at very high field (about -30 ppm). Since only downfield hyperfine shifted peaks were observed in all other Fe-S proteins, the upfield resonances may be unique to high potential 4-Fe centers and originate from protons other than those on the cysteinyl ligands to the cluster. The pH dependences of the chemical shifts of a large number of aromatic and hyperfine-shifted resonances indicate that the ionization state of his-42 exerts an influence on the electronic properties of the cluster despite its being located relatively far away. The oxidation state of the cluster also affects the ionization equilibrium of the histidine; pKa values of 6.7 and 7.3 are measured in the oxidized and reduced protein, respectively. These observations support a previous proposal based on kinetic and visible spectroscopic evidence that the ionization state of his-42 affects the stability and oxidation rate of the reduced cluster.

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