High-potential iron protein, resonance

G Backes, Y Mino, TM Loehr, TE Meyer, MA Cusanovich, WV Sweeny, ET Adman, J Sand-ers-Loehr. The environment of Ee4S4 clusters in ferredoxms and high-potential iron proteins. New information from X-ray crystallography and resonance Raman spectroscopy. J Am Chem Soc 113 2055-2064, 1991. 

Figure 10. Resonance Raman spectrum of the 4Fe-AS-4Cys cluster In reduced high-potential Iron protein from Rhodopseudomonas globlformls. Spectral conditions as In Figure 9, but spectrum of frozen solvent not subtracted out. (From Mlno, Y. Loehr,...

Fluorine-labeled analogues of C. vinosum high-potential iron protein have been investigated by F NMR spectroscopy. By incorporation of specific fluorine-labeled amino acid residues, one can insert unique probes at well-defined locations within the protein core. The synthesis and purification of 2-, 3-, and 4-fluorophenylalanine (abbreviated 2-F-, 3-F-, and 4-F-Phe, respectively), 3-fluorotyrosine (3-F-Tyr), and 5-fluorotr3q)tophan (5-F-Trp) derivatives of C. vinosum HiPIP, the assignment of F NMR resonances, the measurement of longitudinal relaxation times, and the temperature dependence of F and resonances have all been reported 42, 43, 136). These measurements were used to examine structural perturbations of mutants, the dynamics of interaction of residues with the cluster, and solvent accessibility, and as a test of the relative contribution of cross-relaxation to magnetization decay. 

Fig. 8. Resonance Raman spectra of reduced high-potential iron-sulfiir protein from Chromatium vinosum (HiPIP) at room temperature with a spinning NMR tube, laser power 150 mW, spectral slit width 6 cm (top), and as a frozen solution at liquid N2 temperature, laser power 250 mW, spectral slit width 8 cm (bottom). Both spectra were obtained via backscattering with 457.9 nm Ar laser excitation. ...

The 4-Fe proteins show a cubane-like iron-sulfur center with an iron atom at each of the four alternate corners of a distorted cube. The oxidized high-potential 4-Fe cluster is paramagnetic, with Seff = 1/2, and displays a nearly axial EPR spectrum. AK -band ENDOR study of such an iron protein isolated from C. vinosum ( Fe enriched) has been reported by Reid In this microwave frequency region the proton ENDOR signals do not overlap with the Fe resonances. The hfs of Fe were found to be nearly isotropic with coupling values of 22.6 and 32.5 MHz. Similar values have been found by Anderson et al. / from Fe- Fe difference spectra. Since only two different A " tensors were observed, the iron atoms were classified in two pairs of equivalent nuclei. Mdssbauer data show that the two hf couplings are of opposite sign ... 

Fig. 11.1 Relationship among catalytic intermediates of peroxidases. The formal oxidation state of each species is indicated by the numbers +2 to +6. The formal oxidation state of the species directly correlates with the relative energy content of the intermediates. The entry and exit of external electron donors/acceptors is indicated. In spite of its high oxidation state, Compound III is relative inert given the stability provided by the Fe(II) 02, Fe(III) 02 and Fe(IV) 022 resonance forms. Nevertheless, amino acid residues may rescue the free radical of Compound III, restore the iron atom ferric state, and allocate the free radical into a low redox potential site in the protein backbone. When the porphyrin performs as an electron donor, a different reaction occurs, resulting in tetrapyrrole bleaching and iron release...

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