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R Cammack

Publications and source records attributed to R Cammack.

At least 145 records · Page 8Linked to original sources
PubMed1975

Electron paramagnetic resonance studies of cytochrome P-450 in plant microsomes.

The technique of electron paramagnetic resonnance spectrometry has been applied to the study of plant microsomal electron-transport components. Only tulip-bulb microsomes were found to give strong enough signals to allow detailed study. At 77 K in the oxidised state, signals were observed at g values of 2.40, 2.25 and 1.93, characteristic of cytochrome P-450 in the low-spin state, and also at g = 4.27, attributable to ferric iron in a rhombic environment. The signals at g = 2.40, 2.25 and 1.93 disappeared upon reduction with sodium dithionite. At 10 K in the oxidised state, signals at g = 8.3 and 3.3 appeared, and these were attributed to high-spin cytochrome P-450. At this temperature a further signal at g = 6, due to cytochrome P-420, was seen in aged tulip-bulb microsomes. Redox titration of both high-spin and low-spin cytochrome P-450 gave the same apparent midpoint potential of -315 +/- mV at pH 6.8 and 25 degrees C. The significance of this value is discussed. Addition of "type I" or "type II" ligands to oxidized cytochrome P-450 caused an increase and a decrease, respectively, in the ratio of the high-spin to the low-spin form. A second effect of aniline, a type II ligand of cytochrome P-450, was to remove the g = 6 signal, suggesting that it also interacts with cytochrome P-420. No iron-sulphur proteins similar to those found in some other cytochrome P-450 electron-transport chains could be detected in any of the microsomes analysed.

Binding Sites↗
PubMed1975

The iron electron-nuclear double resonance (ENDOR) of 4-Fe clusters in iron-sulfur proteins from Chromatium and Clostridium pasteurianum.

Iron electron-nuclear double resonance (ENDOR) measurements were made of the 4-Fe clusters in oxidized Chromatium high-potential iron-sulfur protein, dithionite-reduced high-potential iron-sulfur protein in 80% dimethylsulphoxide, fully reduced Clostridium pasteurianum ferredoxin in aqueous solution and in 80% dimethylsulfoxide. The hyperfine couplings determined show that: i) the electron distribution in each case is nearly symmetric; ii) there are two types of iron in oxidized high potential iron-sulfur protein; iii) only one type of iron is observed in each fully reduced 4-Fe cluster; iv) the data also suggest a greater electron delocalization onto the ligands as compared to the 2-Fe ferredoxins.

Bacterial Proteins↗
PubMed1975

Equisetum (horsetail) ferredoxin: characterization of the active centre and position of the four cysteine residues in this 2Fe-2S protein.

Analysis of the ferredoxin of the primitive vascular plant Equisetum indicates that the cysteine residue normally found at position 18 of plant-type ferredoxins is replaced by a valine, although the spectroscopic properties of the ferredoxins are unaffected. It is concluded that the iron--sulphur cluster in plant-type ferredoxins is attached to cysteine residues 39, 44, 47 and 77.

Amino Acid Sequence↗
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↗
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↗
PubMed1974

Mössbauer effect in the 'super-reduced' form of the high-potential iron-sulphur protein from Chromatium.

Mössbauer-effect studies of the super-reduced form of Chromatium high-potential iron-sulphur protein indicate that the iron atoms are in a similar valency state to those in reduced ferredoxin from Clostridium pasteurianum, with possibly some inequivalence between the iron atoms within the four-iron centre. Mössbauer spectroscopy also shows magnetic differences between the four-iron centres in the two proteins.

Bacterial Proteins↗
PubMed1974

The development of plastocyanin in greening bean leaves.

The plastocyanin content of etiolated bean leaves (Phaseolus vulgaris L.) was measured, and the development of the protein in response to light was followed. Measurements were made by quantitative extraction of plastocyanin and a sensitive assay with an O(2) electrode. The electron-paramagnetic-resonance (e.p.r.) signal of oxidized plastocyanin was used as an independent check on the validity of the assay method, and on the thoroughness of extraction. After an initial lag period, the amount of plastocyanin in greening bean leaves increased to reach a maximum after 50h illumination. The chlorophyll/plastocyanin ratio reached a maximum value of 200 irrespective of the light intensity at which greening was carried out, suggesting that the synthesis of the two components is co-ordinated. Experiments involving treatment of etiolated seedlings with brief periods of light of different spectral composition indicated that phytochrome is involved in plastocyanin synthesis. The lack of inhibition of plastocyanin synthesis by specific inhibitors of chloroplast protein synthesis suggests that the protein is synthesized on cytoplasmic ribosomes. The data are discussed in relation to the development of ferredoxin in greening bean leaves.

Chlorophyll↗