scholarly journals A study of the oxidized form of Pseudomonas aeruginosa cytochrome c-551 peroxidase with the use of magnetic circular dichroism

1984 ◽  
Vol 223 (2) ◽  
pp. 369-378 ◽  
Author(s):  
N Foote ◽  
J Peterson ◽  
P M A Gadsby ◽  
C Greenwood ◽  
A J Thomson
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Circular Dichroism ◽  
Cytochrome C ◽  
Room Temperature ◽  
Magnetic Circular Dichroism ◽  
Axial Ligand ◽  
Temperature Dependent ◽  
Magnetic Circular Dichroism Spectroscopy ◽  
Different Temperatures ◽  
Circular Dichroïsm

The magnetic properties at different temperatures of oxidized Pseudomonas aeruginosa cytochrome c-551 peroxidase were studied, with the use of the technique of magnetic-circular-dichroism spectroscopy. At 4.2K, both constituent haems were found to be low-spin, and the axial ligand pairs were identified as histidine-histidine and histidine-methionine. At room temperature high-spin signals were observed, amounting to less than 25% of the total haem present. These signals are concluded to arise mainly from a temperature-dependent spin-state equilibrium in the methionine-ligated haem.

scholarly journals The nature of haem a3 in the oxidized state of cytochrome c oxidase. Evidence from low-temperature magnetic-circular-dichroism spectroscopy in the near infrared region

1982 ◽  
Vol 207 (1) ◽  
pp. 167-170 ◽  
Author(s):  
A J Thomson ◽  
D G Englinton ◽  
B C Hill ◽  
C Greenwood
Keyword(s):  
Circular Dichroism ◽  
Cytochrome C ◽  
Cytochrome C Oxidase ◽  
Near Infrared ◽  
Magnetic Circular Dichroism ◽  
Infrared Region ◽  
Magnetic Circular Dichroism Spectroscopy ◽  
Near Infrared Region ◽  
Circular Dichroïsm ◽  
Inhibited Enzyme

The magnetic-circular-dichroism (m.c.d.) spectra of oxidized ‘resting’ bovine cytochrome c oxidase and the cyanide-inhibited form are reported at 5.15 T and at 4.2 K along with m.c.d. magnetization curves plotted at selected wavelengths. In both spectra there are features at 790nm and 1564nm due to Cua and haem a respectively, the e.p.r.-detectable components of the enzyme. There is a new peak at 1946nm only in the spectrum of the cyanide-inhibited enzyme. Arguments are advanced that assign this to low-spin ferric haem a3 bridged to Cua3, thereby forming a ferromagnetically coupled pair of metal ions.

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 Characterization of the partially reduced cyanide-inhibited derivative of cytochrome c oxidase by optical, electron-paramagnetic-resonance and magnetic-circular-dichroism spectroscopy

1981 ◽  
Vol 193 (3) ◽  
pp. 699-708 ◽  
Author(s):  
M K Johnson ◽  
D G Eglinton ◽  
P E Gooding ◽  
C Greenwood ◽  
A J Thomson
Keyword(s):  
Circular Dichroism ◽  
Cytochrome C ◽  
Cytochrome C Oxidase ◽  
Near Infrared ◽  
Magnetic Circular Dichroism ◽  
Circular Dichroism Spectroscopy ◽  
Paramagnetic Resonance ◽  
Magnetic Circular Dichroism Spectroscopy ◽  
Circular Dichroïsm ◽  
Reduced State

Optical. e.p.r. and near-infrared low-temperature m.c.d. (magnetic-circular-dichroism) spectroscopy were used to characterize the partially reduced cyanide-inhibited derivative of cytochrome c oxidase produced by anaerobic reductive titration with dithionite. The reductions of cytochrome a3+ and Cu2+a were followed by observation of the e.p.r. signals at g = 3.03, 2.21 and 1.5 and at g = 2.18, 2.03 and 1.99. As reduction proceeds new e.p.r. signals (g = 3.58 and 1.56) appear that quantify to give one haem per enzyme unit when a small excess of dithionite has been titrated in. The e.p.r. signal of the Cu2+a titrates in parallel with the disappearance of the band and 820nm in the optical absorption spectrum. The near-infrared m.c.d. spectrum shows the presence of the low-spin ferric haem, a3+, in the oxidized state of the enzyme, as a well-resolved positive peak at 1650nm. As reduction proceeds this band is replaced by one at 1550nm due to haem a3+(3)–CN in the partially reduced state. Hence as haem a3+(3)–CN becomes e.p.r.-detectable it also shows a near-infrared m.c.d. spectrum characteristic of a low-spin ferric haem. It is concluded that the partially reduced state of cyanide-inhibited cytochrome c oxidase contains a2+ . Cu+a . a3+(3)–CN . Cu+a3.

scholarly journals A study of the magnetic properties of haem a3 in cytochrome c oxidase by using magnetic-circular-dichroism spectroscopy

1981 ◽  
Vol 193 (3) ◽  
pp. 687-697 ◽  
Author(s):  
A J Thomson ◽  
M K Johnson ◽  
C Greenwood ◽  
P E Gooding
Keyword(s):  
Circular Dichroism ◽  
Cytochrome C ◽  
Cytochrome C Oxidase ◽  
Electronic State ◽  
Ground State ◽  
Magnetic Circular Dichroism ◽  
Circular Dichroism Spectroscopy ◽  
Magnetic Circular Dichroism Spectroscopy ◽  
Spin Singlet ◽  
Circular Dichroïsm

M.c.d. (magnetic-circular-dichroism) spectroscopy was used to study the magnetization properties of the haem centres in cytochrome c oxidase with magnetic fields of between 0 and 5.3 T over the temperature range 1.5–200 K. The oxidized, oxidized cyanide and partially reduced cyanide forms of the enzyme were studied. In the oxidized state only cytochrome a3+ is detectable by m.c.d. spectroscopy, and its magnetization characteristics show it to be a low-spin ferric haem. In the partially reduced cyanide form of the enzyme cytochrome a is in the diamagnetic low-spin ferrous form, whereas cytochrome a3–CN is e.p.r.-detectable and gives an m.c.d.-magnetization curve typical of a low-spin ferric haem. In the oxidized cyanide form of the enzyme both cytochrome a and cytochrome a3–CN are detectable by m.c.d. spectroscopy, although only cytochrome a gives an e.p.r. signal. The magnetization characteristics of haem a3–CN show clearly that its ground state is an electronic doublet and that another state, probably a spin singlet, lies greater than 10 cm-1 above this. These features are well accounted for by an electronic state of spin S = 1 with a predominantly axial distortion, which leaves the doublet, Ms = +/- 1, as the ground state and the component Ms = 0 as the excited state. This state would not give an e.p.r. signal. Such an electronic state could arise either from a ferromagnetic coupling between haem a3+(3)-CN and the cupric ion, Cua3, or form a haem in the Fe(IV) state.

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