Spectroscopic and magnetic characterization of the high potential iron-sulfur protein from Chromatium

Cerdonio, M.; Wang, Run-Han; Rawlings, J.; Gray, Harry B.

doi:10.1021/ja00827a057

Cited by 19 publications

(12 citation statements)

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“…Using difference spectroscopy, Eaton et al (Eaton & Lovenberg, 1970;Eaton et al, 1971) have observed weak d -*• d transitions in the near-IR ( > 1000 nm) in reduced rubredoxin and reduced 2-Fe ferredoxins, confirming the existence of tetrahedral Fe(II) in these cases, and this work was extended to other proteins by Kimura et al (Tang et al, 1973;Mukai et al, 1974). Cerdonio et al (1974) have attempted to observe analogous transitions in reduced HIPIP; the lack of success was attributed to the existence of a delocalized electronic structure in which separate Fe(II) and Fe(III) oxidation states do not exist.…”

supporting

confidence: 57%

“…VOL. 17 ( Cerdonio et al, 1974). The 9600-cm-1 band in the spectrum of reduced HIPIP (Figure 5) is also clearly visible in the absorption spectra of oxidized Bacillus stearothermophilus ferredoxin (Figure 7) and Clostridium pasteurianum ferredoxin (Figure 6), although less well resolved in the latter two cases.…”

Section: Resultsmentioning

confidence: 91%

“…The CD in particular reveals a multiplicity of bands in the regions where electronic absorption is weak and obscured by vibrational transitions. Previous workers have been unable to observe electronic transitions in this region in the case of reduced HIPIP and erroneously concluded they were absent (Cerdonio et al, 1974). Conclusions about the appropriateness of theoretical electronic structural models drawn from the absence of transitions in this region must therefore be reexamined.…”

Section: Resultsmentioning

confidence: 94%

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Circular dichroism and magnetic circular dichroism of iron-sulfur proteins

Stephens¹,

Thomson²,

Dunn³

et al. 1978

Biochemistry

132

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Circular dichroism (CD) and magnetic circular dichroism (MCD) spectra are reported for the 2-Fe ferredoxins from Pseudomonas putida and Spirulina maxima, Chromatium HIPIP, the 4-Fe ferredoxin from Bacillus stearothermophilus, and the 8-Fe ferredoxin from Clostridium pasteurianum. The spectral range spans the near-infrared, visible, and near ultraviolet. In all cases except oxidized 2-Fe ferredoxins, electronic absorption is observed continuously from less than 5000 cm-1 to above 30,000 cm-1. The CD spectra of the two 2-Fe ferredoxins are similar. In contrast, the CD of the 4-Fe and 8-Fe proteins, for a given 4-Fe cluster oxidation level, varies considerable with protein. MCD is less sensitive to protein environment than is CD. In the 2-Fe proteins, MCD at 5 T is appreciably smaller than the CD; in the 4-Fe and 8-Fe proteins, MCD and CD are comparable in magnitude. Both CD and MCD are more highly structured than the corresponding absorption spectra. The CD and MCD spectra reported provide a broader base than heretofore available for the characterization of iron-sulfur proteins containing 2-Fe and 4-Fe clusters and for the evaluation of electronic structural models for these clusters.

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supporting

confidence: 57%

Section: Resultsmentioning

confidence: 91%

Section: Resultsmentioning

confidence: 94%

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Circular dichroism and magnetic circular dichroism of iron-sulfur proteins

Stephens¹,

Thomson²,

Dunn³

et al. 1978

Biochemistry

132

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“…Natural CD spectra (3) Madison, WI. 1 1 In addition to the well-known "390" band, all C2-state proteins exhibit a variably resolved peak at -v9600 cm-' (-u1050 nm); this band has been previously reported (6) (11). In the reduced clusters, the CD (11) shows that electronic transitions exist to well below 5000 cm-1; the lack of observation of MCD here is due to the small magnitude of the MCD anisotropy ratio.…”

supporting

confidence: 49%

Cluster characterization in iron-sulfur proteins by magnetic circular dichroism.

Stephens¹,

Thomson²,

Keiderling³

et al. 1978

Proc. Natl. Acad. Sci. U.S.A.

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We report magnetic circular dichroism (MCD) spectra of 4-Fe iron-sulfur clusters in the iron-sulfur proteins Chromatium high-potential iron protein (HIPIP) show that:(i) MCD is measurable throughout the near-infrared-visible-ultraviolet spectral range (2000-300 nm) in all three accessible oxidation states (n = 1, 2, 3; henceforth referred to as C'-, C2-, and C3-).(ii) Like the absorption spectra, but unlike the natural circular dichroism (CD) spectra, the MCD spectrum is characteristic of the cluster oxidation state and insensitive to the specific protein to which the cluster is bound. Unlike the absorption spectra, but like the natural CD spectra, the MCD spectrum exhibits appreciably structured features.(iii) The MCD spectra of the 4-Fe clusters are distinguishable from those of the 2-Fe clusters [Fe2S2(SR)4]n-(n = 2, 3).(iv) MCD is usable for the differentiation of 2-Fe and 4-Fe iron-sulfur clusters in iron-sulfur proteins.MCD measurements are reported for the iron-sulfur proteins Chromatium high-potential iron protein (HIPIP), Bacillus stearothermophilus ferredoxin (Bs ferredoxin), and Clostridium pasteurianum ferredoxin (Cp ferredoxin). In HIPIP the single cluster was studied in the C'-and C2-oxidation states.In Bs ferredoxin, which contains a single cluster, and in Cp ferredoxin, which contains two clusters, the C2-and C3-oxidation states were studied. All measurements were made on aqueous solutions at room temperature; experiments in the near-infrared required substitution of 2H20 for H20. Oxidation of reduced HIPIP was carried out by using K3Fe(CN)6. Oxidized Bs and Cp ferredoxins were reduced with Na2S204. Reduced Bs and Cp ferredoxins were handled anaerobically. MCD was measured by using a Cary 61 and an infrared CD instrument described previously (4, 5) and at magnetic fields of approximately 40 kilogauss (1 G = 10-4 T). Natural CD spectra (3) In all three oxidation states (C'-, C2-, C3-) MCD is observed down to the lowest energies (below 5000 cm'1) attained.ttOther features of note are the unusual monosignate nature of all MCD and the comparable magnitude of the MCD in paramagnetic (C'-, C3-) and diamagnetic (C2-) clusters. MCD has been reported for the 2-Fe iron-sulfur proteins spinach ferredoxin, adrenodoxin, and Spirulina maxima ferredoxin (8-10). We have repeated these measurements and extended them to include near-infrared wavelengths and to putidaredoxin (3). As in the 4-Fe proteins, the MCD is not very sensitive to the specific protein but varies with cluster oxidation state. The 2-Fe cluster MCD spectra are distinguishably different from those of the 4-Fe clusters. In particular, unlike the Abbreviations: MCD, magnetic circular dichroism; CD, natural circular dichroism; HIPIP, high-potential iron protein; Bs ferredoxin, ferredoxin from Bacillus stearothermophilus; Cp ferredoxin, ferredoxin from Clostridium pasteurianum. t Permanent address:

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“…Solutions of salts of [Fe4S4(SR)4]3_ were prepared under an argon atmosphere using thoroughly dired and degassed solvents, and were sealed in quartz EPR tubes under vacuum. Spectra were recorded as soon as possible after sample preparation; however, independent experiments (49) •6.49 (56) 1.74 (66) 1.26 (62) •2.58 (64) • 1.37 (59) 6.89(53) •6.99(49) 6.67 (52) •1.46(53) 6.69 (69) • 1.99 (68) • 1.36( 57 revealed that solutions in sealed tubes stored at liquid nitrogen temperature appear to be stable for an indefinite period of time. Spectra were recorded at modulation frequencies in the range 103-10s Hz as a check for fast passage effects, but line shapes were found to be invariant over this range.…”

Section: Introductionmentioning

confidence: 99%