Search PubMed⌕ Search

Biomedical subjects

D O Hall

Publications and source records attributed to D O Hall.

At least 109 records · Page 6Linked to original sources
PubMed1972

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

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.

Amino Acid Sequence↗
PubMed1971

Mössbauer effect in Scenedesmus and spinach ferredoxins. The mechanism of electron transfer in plant-type iron-sulphur proteins.

1. The Mössbauer spectra of Scenedesmus ferredoxin enriched in (57)Fe were measured and found to be identical with those of two other plant-type ferredoxins (from spinach and Euglena) that had been previously measured. Better resolved Mössbauer spectra of spinach ferredoxin are also reported from protein enriched in (57)Fe. All these iron-sulphur proteins are known to contain two iron atoms in a molecule that takes up one electron on reduction. 2. The Mössbauer spectra at 195 degrees K have electric hyperfine structure only and show that on reduction the electron goes to one of the iron atoms, the other appearing to remain unchanged. 3. In the oxidized state, both iron atoms are in a similar chemical state, which appears from the chemical shift and quadrupole splitting to be high-spin Fe(3+), but they are in slightly different environments. In the reduced state the iron atoms are different and the molecule appears to contain one high-spin Fe(2+) and one high-spin Fe(3+) atom. 4. At lower temperatures (77 and 4.2 degrees K) the spectra of both iron atoms in the reduced proteins show magnetic hyperfine structure which suggests that the iron in the oxidized state also has unpaired electrons. This provides experimental evidence for earlier suggestions that in the oxidized state there is antiferromagnetic exchange coupling, which would result in a low value for the magnetic susceptibility. 5. In a small magnetic field the spectrum of the reduced ferredoxin shows a Zeeman splitting with hyperfine field (H(n)) of 180kG at the nuclei. On application of a strong magnetic field H the spectrum splits into two spectra with effective fields H(n)+/-H, thus confirming the presence of the two antiferromagnetically coupled iron atoms. 6. These results are in agreement with the model proposed by Gibson, Hall, Thornley & Whatley (1966); in the oxidized state there are two Fe(3+) atoms (high spin) antiferromagnetically coupled and on reduction of the ferredoxin by one electron one of the ferric atoms becomes Fe(2+) (high spin).

Chlorophyta↗
PubMed1971

Mössbauer studies of adrenodoxin. The mechanism of electron transfer in a hydroxylase iron-sulphur protein.

1. Mössbauer spectra were measured of adrenodoxin purified from porcine adrenal glands. They show similarities to the spectra of the plant ferredoxins. All of these proteins contain two atoms of iron and two of inorganic sulphide per molecule, and on reduction accept one electron. 2. As with the plant ferredoxins the adrenodoxin for these measurements was enriched with (57)Fe by reconstitution of the apo-protein, and subsequently was carefully purified and checked by a number of methods to ensure that it was in the same conformation as the native protein and contained no extraneous iron. 3. The Mössbauer spectra of oxidized adrenodoxin at temperatures from 4.2 degrees K to 197 degrees K show that the iron atoms are probably high-spin Fe(3+), and in similar environments, and experience little or no magnetic field from the electrons. 4. Mössbauer spectra of reduced adrenodoxin showed magnetic hyperfine structure at all temperatures from 1.7 degrees K to 244 degrees K, in contrast with the reduced plant ferredoxins, which showed it only at lower temperatures. This is a consequence of a longer electron-spin relaxation time in reduced adrenodoxin. 5. At 4.2 degrees K in a small magnetic field the spectrum of reduced adrenodoxin shows a sixline Zeeman pattern due to Fe(3+) superimposed upon a combined magnetic and quadrupole spectrum due to Fe(2+). 6. In a large magnetic field (30kG) each hyperfine pattern is further split into two. Analysis of these spectra at 4.2 degrees K and 1.7 degrees K shows that the effective fields at the Fe(3+) and Fe(2+) nuclei are in opposite directions. This agrees with the proposal, first made for the ferredoxins, that the iron atoms are antiferromagnetically coupled. 7. In accord with the model for the ferredoxins, it is proposed that the oxidized adrenodoxin contains two high-spin Fe(3+) atoms which are antiferromagnetically coupled; on reduction one iron atom becomes high-spin Fe(2+).

Adrenal Glands↗
PubMed1969

Mossbauer spectroscopy of the iron-sulfur proteins.

The Mössbauer spectra of (57)Fe in two plant ferredoxins (from spinach and Euglena) and in xanthine oxidase have been measured at a series of temperatures and magnetic fields, and are found to be similar in all three proteins. In the oxidized state the iron is nonmagnetic. In the reduced state, the iron nuclei show magnetic hyperfine interaction with an electron spin S of (1/2), producing an effective field of about 180 kG at the nuclei.

Euglena↗