Mössbauer effect in rubredoxin. Determination of the hyperfine field of the iron in a simple iron–sulphur protein

Abstract

1. Rubredoxin isolated from the green photosynthetic bacterium Chloropseudomonas ethylica was similar in composition to those from anaerobic fermentative bacteria. Amino acid analysis indicated a minimum molecular weight of 6352 with one iron atom per molecule. 2. The circular-dichroism and electron-paramagnetic-resonance spectra of Ch. ethylica rubredoxin showed many similarities to those of Clostridium pasteurianum, but suggested that there may be subtle differences in the protein conformation about the iron atom. 3. Mössbauer-effect measurements on rubredoxin from Cl. pasteurianum and Ch. ethylica showed that in the oxidized state the iron (high-spin Fe(3+)) has a hyperfine field of 370+/-3kG, whereas in the reduced state (high-spin Fe(2+)) the hyperfine field tensor is anisotropic with a component perpendicular to the symmetry axis of the ion of about -200kG. For the reduced protein the sign of the electric-field gradient is negative, i.e. the ground state of the Fe(2+) is a [unk] orbital. There is a large non-cubic ligand-field splitting (Delta/k=900 degrees K), and a small spin-orbit splitting (D~+4.4cm(-1)) of the Fe(2+) levels. 4. The contributions of core polarization to the hyperfine field in the Fe(3+) and Fe(2+) ions are estimated to be -370 and -300kG respectively. 5. The significance of these results in interpretation of the Mössbauer spectra of other iron-sulphur proteins is discussed.

Structure and Mechanistic Insights into Novel Iron-mediated Moonlighting Functions of Human J-protein Cochaperone, Dph4

“…1 B ). The resonances at g ∼4.3 and g ∼9.14 are characteristic of high spin Fe 3+ ion in tetrahedral geometry as reported previously for oxidized rubredoxins ( 17 ). Furthermore, both of the signals were found to be sensitive to temperature, similar to rubredoxins ( 18 ) ( Fig.…”

Rubredoxin from the Green Sulfur Bacterium Chlorobium tepidum Functions as an Electron Acceptor for Pyruvate Ferredoxin Oxidoreductase

“…1A); at 492 nm, the absorption coefficient was 6.89 mM Ϫ1 cm Ϫ1 , calculated using a molecular weight of 6,500. C. tepidum Rd differed from other bacterial Rds by the presence of at least two absorption bands in the 300 -400 nm region, a property that may be unique to only green photosynthetic bacteria (32,33). The A 492 /A 280 ratio was 0.343.…”

The DnaJ proteins DJA6 and DJA5 are essential for chloroplast iron–sulfur cluster biogenesis

“…Each protein was brownish with a typical peak at 420 nm (Fig EV3A and B), indicating that the absorbance spectrum of DJA6 and DJA5 was derived from bound iron, but not from an iron–sulfur center (Yabe et al , 2004; Bandyopadhyay et al , 2008; Schwenkert et al , 2009; Gao et al , 2013). A resonance at g ~ 4.3 was observed in DJA6 and DJA5 proteins by electron paramagnetic resonance spectroscopy (EPR) (Fig 4B), characteristic of a high spin ferric iron in tetrahedral geometry of oxidized rubredoxins (Rao et al , 1972; Arnold et al , 2016).…”