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Biomedical subjects

C E Johnson

Publications and source records attributed to C E Johnson.

At least 181 records · Page 10Linked to original sources
PubMed1975

X-ray photoelectron spectra of iron-sulphur proteins.

The X-ray photoelectron spectra of the 2p, 3s and 3p levels of iron in oxidized Clostridium pasteurianum ferredoxin indicate that the eight iron atoms in the molecule are indistinguishable. Their magnetic state is indicated both by core polarization splitting of the 3s electrons, and by "shake-up' satellites on the 2p lines. Similar satellites are observed in the 2p lines of reduced Chromatium high-potential iron-sulphur proteins and oxidized spinach ferredoxin, indicating that there too the iron atoms are magnetic. The low observed magnetic susceptibility of these proteins is therefore due to spin-coupling between the iron atoms in the active centre.

Chromatium↗
PubMed1975

Physicochemical characterization of the four-iron-four-sulphide ferredoxin from Bacillus stearothermophilus.

1. A stable ferredoxin was prepared from Bacillus stearothermophilus and purified by chromatography on DEAE-cellulose and by electrophoresis. 2. The minimum molecular weight determined from the amino acid composition was about 7900 and this was in reasonable agreement with a value of 8500 determined by polyacrylamide-gel electrophoresis. The ferredoxin contained four iron atoms and four labile sulphide groups per molecule. 3. The optical absorption, optical-rotatory-dispersion and circular-dichroism spectra are typical of ferredoxins containing 4Fe-4S clusters. 4. Oxidation-reduction titrations, combined with electron-paramagnetic-resonance (e.p.r.) spectroscopy, showed that the protein has a mid-point potential, at pH8, of -280 +/- 10mV, and that only one electron-accepting paramagnetic species is present. 5. The e.p.r. spectrum of the reduced ferredoxin is more readily saturated with microwave power at low temperatures than those of the eight-iron ferredoxins, indicating that there is another mechanism of electron-spin relaxation in the latter. 6. Mossbauer spectra of both redox states were observed over a range of temperatures and in magnetic fields. At high temperatures (77 degrees K and above) both redox states appear as quadrupole-split doublets; in the reduced state two resolved doublets are seen, suggesting appreciable localization of the additional reducing electron. 7. The average chemical shift indicates formal valences of two Fe3+ and two Fe2+ in the oxidized state and three Fe2+ and one Fe3+ in the reduced state. However, the spectra indicate that there are differing degrees of electron delocalization over the iron atoms. 8. At low temperatures (4.2 degrees K) the oxidized form shows no hyperfine magnetic interaction, even in an applied magnetic field, evidence that the oxidized ferredoxin is in a non-magnetic state as a result of antiferromagnetic coupling between the iron atoms. 9. At 4.2 degrees K the reduced form shows a broad asymmetric pattern resulting from magnetic hyperfine interaction. This contrasts with the reduced ferredoxin of Clostridium pasteurianum, which shows a doublet, suggesting that in the latter there may be interaction between the two 4Fe-4S centres. 10. In large applied magnetic fields, positive and negative hyperfine fields are seen in the Mossbauer spectra of the reduced ferredoxin, evidence for antiferromagnetic coupling between the iron atoms in the 4Fe-4S centre. The high-field spectra of the reduced ferredoxin of B. stearothermophilus are similar to those of the reduced ferredoxin of C. pasteurianum.

Amino Acids↗
PubMed1975

Prophylactic use of hydroxyprogesterone caproate in abdominal surgery during pregnancy. A retrospective evaluation.

Abdominal surgery (unrelated to delivery) during pregnancy is not common. Review of a recent 17-year experience at our institution revealed 112 surgical procedures among 25,189 deliveries--an incidence of 0.44% (1 case for every 225 deliveries). Progestational agents have been used prophylactically in such procedures, but few studies have adequately assessed the effectiveness of these drugs to prevent onset of premature labor. The present study involved 35 gravid patients who had been treated with various doses of hydroxyprogesterone caproate before and after operations unrelated to delivery. These 35 patients were matched with 35 gravid control patients who had undergone similar operations but who had not received progestational compounds. Analysis revealed no significant difference in the abortion rate between these two groups.

Abortion, Spontaneous↗
PubMed1975

Cholecystectomy in pregnancy.

During the 17 years 1955 through 1971, 20 gravid patients underwent cholecystectomy. This represented 1 case for every 1259 deliveries (0.079% of 25,189 deliveries). The primary indication for surgery was repeated attacks of gallbladder colic. Generally, surgery was performed between the 10th and the 20th week of gestation. There was one spontaneous abortion; this occurred at 10 weeks of gestation, 42 days after surgery.

Abortion, Spontaneous↗
PubMed1974

Mössbauer effect in the eight-iron ferredoxin from Clostridium pasterurianum. Evidence for the state of the iron atoms.

1. Mössbauer spectra of both redox states of the eight-iron ferredoxin from Clostridium pasteurianum were observed over a range of temperatures and in magnetic fields. 2. At high temperatures (77 degrees K and above) the spectra of both states consist essentially of the superposition of two or more closely similar doublets. 3. The average chemical shift for the oxidized protein leads to the proposal that each of the two four-iron active centres consists formally of two Fe(3+) and two Fe(2+) atoms. 4. The average chemical shift and quadrupole splitting increase on reduction, consistent with there being one Fe(3+) and three Fe(2+) atoms per centre in the reduced molecule. 5. The spectral changes on reduction show that all the iron atoms are affected when one electron is added to each four-iron centre. 6. No separate Fe(3+) and Fe(2+) spectra were observed (as they were, for instance, in the reduced two-iron plant ferredoxins) suggesting that the d electrons are not localized on particular atoms, but are shared approximately equally by all four atoms in the four-iron centres. 7. At low temperatures (4 degrees K and below) no magnetic hyperfine interaction was observed in the oxidized protein even in an applied magnetic field, confirming the non-magnetic nature of the molecule in the oxidized state, and suggesting that the four iron atoms in each centre are antiferromagnetically coupled together to give zero spin. 8. Magnetic hyperfine interaction was observed in the reduced protein at low temperatures, and showed that all the iron atoms were magnetic. This demonstrates that one electron goes to each centre on reduction. 9. On application of a large magnetic field to the reduced protein at low temperatures, both positive and negative hyperfine fields were shown to be present, thus directly showing that antiferromagnetic coupling exists between the iron atoms in the reduced state.

Binding Sites↗
PubMed1974

Mössbauer effect in the high-potential iron-sulphur protein from Chromatium. Evidence for the state of the iron atoms.

1. The previous Mössbauer work on Chromatium high-potential iron-sulphur protein by Moss et al. (1968) and Evans et al. (1970) was extended to high applied magnetic fields. 2. Measurements of the reduced protein confirm that it is non-magnetic. 3. Spectra of the oxidized protein in applied magnetic fields clearly indicate that some iron atoms have a positive hyperfine field, which is evidence for antiferromagnetic coupling. 4. The spectra can be interpreted in terms of two types of iron atom with positive and negative hyperfine fields of 9 and 12T respectively. 5. A consideration of the chemical shifts and other evidence suggests formal valences of two Fe(3+) and two Fe(2+) atoms in the non-magnetic reduced state, and three Fe(3+) atoms and one Fe(2+) atom in the oxidized state. 6. However, no separate Fe(3+) and Fe(2+) spectra are seen, suggesting that the d electrons are not localized on particular iron atoms.

Bacterial Proteins↗
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↗