scholarly journals Cytochrome c″ isolated from Methylophilus methylotrophus. An example of bis-histidine-co-ordinated Fe3+ haem, with near-perpendicular orientation of the ligands

1990 ◽  
Vol 270 (2) ◽  
pp. 413-417 ◽  
Author(s):  
M J Berry ◽  
S J George ◽  
A J Thomson ◽  
H Santos ◽  
D L Turner
Keyword(s):  
Low Temperature ◽  
Cytochrome C ◽  
High Spin ◽  
Magnetic Circular Dichroism ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Water Soluble ◽  
Reduced Form ◽  
Resonance Spectroscopy ◽  
Methylophilus Methylotrophus ◽  
Perpendicular Orientation

Cytochrome c″ (Methylophilus methylotrophus) is a soluble protein, Mr 15,000, possessing one haem which is high-spin in the reduced state but switches to a low-spin form on oxidation. Low-temperature electron-paramagnetic-resonance spectroscopy of the oxidized state shows a low-spin signal at gz = 3.65 with a folded line-shape typical of a haem of low rhombicity, and the near-infrared magnetic-circular-dichroism (m.c.d.) spectra reveal an unusually intense (delta epsilon = 400 M-1.cm-1 at 5 T, 4.2 K) charge-transfer band at 1560 nm, establishing that the oxidized haem is co-ordinated by two His residues in a near-perpendicular orientation. This conformation is well established for transmembrane b cytochromes, but this appears to be the first example in a water-soluble cytochrome. The low-temperature m.c.d. spectra of the reduced form of the protein confirms that the haem contains a high-spin Fe2+ ligated by one His residue. The redox-linked spin-state change releases a His group. Since this residue is likely to bind a proton at pH values less than 6.5, this cytochrome may provide a useful model of a molecular mechanism of a redox-linked proton uptake and release process.

scholarly journals Some magnetic properties of Pseudomonas cytochrome oxidase

1979 ◽  
Vol 177 (1) ◽  
pp. 29-39 ◽  
Author(s):  
T A Walsh ◽  
M K Johnson ◽  
C Greenwood ◽  
D Barber ◽  
J P Springall ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Cytochrome C ◽  
Cytochrome Oxidase ◽  
Magnetic Circular Dichroism ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Resonance Spectroscopy ◽  
Parallel Study ◽  
Paramagnetic Resonance ◽  
Redox States ◽  
Electron Paramagnetic

The magnetic properties of the haem groups of Pseudomonas cytochrome oxidase and its cyanide-bound derivatives were studied in both the oxidized and reduced states by means of m.c.d. (magnetic circular dichroism) at low temperatures. In addition, the oxidized forms of the enzyme were also investigated by e.p.r. (electron-paramagnetic-resonance) spectroscopy, and a parallel study, using both e.p.r. and m.c.d., was made on Pseudomonas cytochrome c-551 to aid spectral assignments. For ascorbate-reduced Pseudomonas cytochrome oxidase, the temperature-independence of those features in the m.c.d. spectrum corresponding to the haem c, and the temperature-dependence of those signals corresponding to the haem d1, showed the former to be low-spin and the latter to be high-spin (s = 2). However, addition of cyanide to the reduced enzyme gave a form of the protein that was completely low-spin. The e.p.r. and m.c.d. sectra of oxidized Pseudomonas cytochrome oxidase and its cyanide derivative were consistent with the haem c and d1 components being low-spin in both cases. Pseudomonas cytochrome c-551 was found to be low-spin in both its oxidized and reduced redox states.

scholarly journals Low-temperature studies on mixed-valence cytochrome oxidase by using magnetic circular dichroism

1976 ◽  
Vol 159 (3) ◽  
pp. 811-813 ◽  
Author(s):  
T Brittain ◽  
J Springall ◽  
C Greenwood ◽  
A J Thomson
Keyword(s):  
Circular Dichroism ◽  
Low Temperature ◽  
Cytochrome Oxidase ◽  
High Spin ◽  
Room Temperature ◽  
Magnetic Circular Dichroism ◽  
Mixed Valence ◽  
Spin States ◽  
High Spin States ◽  
Circular Dichroïsm

The spin states of the haem components of mixed-valence cytochrome oxidase were studied at room temperature and at temperature down to 20K by using magnetic circular dichroism. The room-temperature studies show the presence of a low-spin ferrous haem together with a low-spin ferric haem, which we attribute to heams a3 and a respectively. At temperatures below 100K it appears that the CO of the mixed-valence CO complex may be irreversibly photolysed, and that in this case haems a and a3 assume their high-spin states. Thus in this enzyme haem-haem interactions appear possible at temperatures below 100K.

scholarly journals The nature of species prepared by photolysis of half-reduced, fully reduced and fully reduced carbonmonoxy-cytochrome c-551 peroxidase from Pseudomonas aeruginosa

1984 ◽  
Vol 223 (2) ◽  
pp. 379-391 ◽  
Author(s):  
C Greenwood ◽  
N Foote ◽  
J Peterson ◽  
A J Thomson
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Fine Structure ◽  
Low Temperature ◽  
Cytochrome C ◽  
Activation Barrier ◽  
Magnetic Circular Dichroism ◽  
High Potential ◽  
Quantum Mechanical ◽  
Methionine Residue ◽  
Magnetic Circular Dichroism Spectroscopy

The half-reduced, fully reduced and fully reduced CO-bound forms of the enzyme cytochrome c-551 peroxidase isolated from Pseudomonas aeruginosa were examined by a combination of low-temperature absorption and magnetic-circular-dichroism spectroscopy. Deliberate low-temperature (4.2K) photolysis of these forms of the enzyme, in all of which the high-potential haem is in the ferrous state, revealed that this haem group, assigned to have a histidine-methionine ligand set, is photosensitive. The photolabile ligand is most likely to be the methionine residue, and the product of photolysis, namely the high-spin (S = 2) ferrous form, is stable at low temperature (4.2K). Warming to approx. 20K allows thermal recombination to occur, restoring the low-spin (S = 0) state. The low-potential haem (bis-histidine ligation) is photoinert in both ferric and ferrous states; however, the photosensitive CO adduct of this centre cannot be maintained as the photolysed (S = 2) product at 4.2K. This surprising observation may be due to quantum-mechanical tunnelling of the CO through the activation barrier even at 4.2K, implying that the activation barrier to thermal recombination is both narrow and low. Low-temperature absorption spectroscopy reveals that the high-potential haem has a very characteristic low-spin ferrous spectrum with intense highly structured beta- and split alpha-bands, whereas the spectrum of the low-potential ferrous haem contains alpha- and beta-bands devoid of fine structure.

scholarly journals The optical properties of CuA in bovine cytochrome c oxidase determined by low-temperature magnetic-circular-dichroism spectroscopy

1983 ◽  
Vol 215 (2) ◽  
pp. 303-316 ◽  
Author(s):  
C Greenwood ◽  
B C Hill ◽  
D Barber ◽  
D G Eglinton ◽  
A J Thomson
Keyword(s):  
Circular Dichroism ◽  
Low Temperature ◽  
Cytochrome C ◽  
Cytochrome C Oxidase ◽  
Magnetic Circular Dichroism ◽  
Paramagnetic Species ◽  
Type I ◽  
Magnetization Curves ◽  
Magnetic Circular Dichroism Spectroscopy ◽  
Circular Dichroïsm

The visible-near-i.r.-region m.c.d. (magnetic-circular-dichroism) spectrum recorded at low temperature in the range 450-900 nm is reported for oxidized resting mammalian cytochrome c oxidase. M.c.d. magnetization curves determined at different wavelengths reveal the presence of two paramagnetic species. Curves at 576, 613 and 640 nm fit well to those expected for an x,y-polarized haem transition with g values of 3.03, 2.21 and 1.45, i.e. cytochrome a3+. The m.c.d. features at 515, 785 and 817 nm magnetize as a S = 1/2 paramagnet with average g values close to 2, and simulated m.c.d. magnetization curves obtained by using the observed g values of CuA2+, i.e. 2.18, 2.03 and 1.99, fit well to the experimental observations. The form of the m.c.d. magnetization curve at 466 nm is curious, but it can be explained if CuA2+ and cytochrome a3+ contribute with oppositely signed bands at this wavelength. By comparing the m.c.d. spectrum of the enzyme with that of extracted haem a-bisimidazole complex it has been possible to deconvolute the m.c.d. spectrum of CuA2+, which shows transitions throughout the spectral region from 450 to 950 nm. The m.c.d.-spectral properties of CuA2+ were compared with those of a well-defined type I blue copper centre in azurin isolated from Pseudomonas aeruginosa. The absolute intensities of the m.c.d. signals at equal fields and temperatures for CuA2+ are 10-20-fold greater than those for azurin. The optical spectrum of CuA2+ strongly suggests an assignment as a d9 ion rather than Cu(I) bound to a thiyl radical.

scholarly journals Azotobacter chroococcum 7Fe ferredoxin. Two pH-dependent forms of the reduced 3Fe clusters and its conversion to a 4Fe cluster

1984 ◽  
Vol 224 (1) ◽  
pp. 247-251 ◽  
Author(s):  
S J George ◽  
A J M Richards ◽  
A J Thomson ◽  
M G Yates
Keyword(s):  
Magnetic Circular Dichroism ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Iron Chelator ◽  
Anaerobic Treatment ◽  
Azotobacter Chroococcum ◽  
Resonance Spectroscopy ◽  
Paramagnetic Resonance ◽  
High Affinity ◽  
Ph Dependent ◽  
Electron Paramagnetic

Ferredoxin from Azotobacter chroococcum has been studied by low-temperature magnetic-circular-dichroism and electron-paramagnetic-resonance spectroscopy. When aerobically isolated ferredoxin contains a [3Fe-4S] and [4Fe-4S] cluster. Anaerobic treatment with dithionite in the presence of ethanediol reduces the [3Fe-4S] cluster to give two spectroscopically distinct forms RI and RII which are reversibly interconvertible with a pKa approximately 7.5. The higher-pH form, RII, has a high affinity for ferrous ion and converts readily to a [4Fe-4S]1+ cluster, scavenging iron from the medium. The presence of the iron chelator EDTA inhibits this conversion.

scholarly journals Magnetization curves of haemoproteins measured by low-temperature magnetic-circular-dichroism spectroscopy

1980 ◽  
Vol 191 (2) ◽  
pp. 411-420 ◽  
Author(s):  
A J Thomson ◽  
M K Johnson
Keyword(s):  
Circular Dichroism ◽  
Cytochrome C ◽  
High Spin ◽  
Ground State ◽  
Magnetic Circular Dichroism ◽  
Striking Difference ◽  
Zero Field ◽  
Magnetization Curves ◽  
Horse Heart Cytochrome ◽  
Circular Dichroïsm

The magnetic-circular-dichroism (m.c.d.) spectra of methymyoglobin cyanide and oxidized horse heart cytochrome c were measured in the region of the Soret band over a range of temperatures from 1.5 to 50 K and in fields from 0 to 5T. A similar study has been made with reduced bovine heart cytochrome c oxidase, which contains one high-spin ferrous haem, namely a3. M.c.d. magnetization curves characteristic of an isolated Kramer's ground state with spin S = 1/2. These curves contrast with the magnetization curve of the high-spin ferrous haem with spin S = 2. The electronic ground state of the latter compound contains zero-field components that are thermally accessible over the temperature range of the experiment. Hence the magnetization curves are a complex nested set. The magnetization curves of the S = 1/2 proteins were analysed and it is shown that it is possible to make estimates of the ground-state g-factors even in the presence of rhombic anisotropy, provided that some knowledge of the polarizations of the electronic transitions is available. The striking difference between the m.c.d. magnetization curves of a simple S = 1/2 paramagnet and magnetically complex ground state should prove extremely useful when m.c.d. spectroscopy is sued to probe the magentic properties of metal centres in proteins, and should have wide application beyond the field of haemoproteins.

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