Heme spin-states of cytochrome c
 oxidase derived from room temperature magnetic susceptibility measurements

The measured room temperature magnetic susceptibility of a bulk sample of buckytubes (buckybundle) is −10.75 × 10−6 emu/g for the magnetic field parallel to the buckybundle axis, which is approximately 1.1 times the perpendicular value and 30 times larger than that of C60. The experimental results are discussed in terms of a graphite-like electronic structure model.

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Near-infrared magnetic and natural circular dichroism of cytochrome c oxidase

Biochemical Journal ◽

10.1042/bj1910319 ◽

1980 ◽

Vol 191 (2) ◽

pp. 319-331 ◽

Cited By ~ 37

Author(s):

D G Eglinton ◽

M K Johnson ◽

A J Thomson ◽

P E Gooding ◽

C Greenwood

Keyword(s):

Cytochrome C ◽

Absorption Band ◽

Cytochrome C Oxidase ◽

High Spin ◽

Room Temperature ◽

Near Infrared ◽

Sodium Dithionite ◽

Cyanide Ion ◽

Reduced State

A detailed study is presented of the room-temperature absorption, natural and magnetic circulation-dichroism (c.d. and m.c.d.) spectra of cytochrome c oxidase and a number of its derivatives in the wavelength range 700-1900 nm. The spectra of the reduced enzyme show a strong negative c.d. band peaking at 1100nm arising from low-spin ferrous haem a and a positive m.c.d. peak at 780nm assigned to high-spin ferrous haem a3. Addition of cyanide ion doubles the intensity of the low-spin ferrous haem c.d. band and abolishes reduced carbonmonoxy derivative the haem a32+-CO group shows no c.d. or m.c.d. bands at wavelengths longer than 700nm. A comparison of the m.c.d. spectra of the oxidized and cyanide-bound oxidized forms enables bands characteristic of the high-spin ferric form of haem a33+ to be identified between 700 and 1300nm. At wavelengths longer than 1300nm a broad positive m.c.d. spectrum, peaking at 1600nm, is observed. By comparison with the m.c.d. spectrum of an extracted haem a-bis-imidazole complex this m.c.d. peak is assigned to one low-spin ferric haem, namely haem a3+. On binding of cyanide to the oxidized form of the enzyme a new, weak, m.c.d. signal appears, which is assigned to the low-spin ferric haem a33+-CN species. A reductive titration, with sodium dithionite, of the cyanide-bound form of the enzyme leads to a partially reduced state in which low-spin haem a2+ is detected by means of an intense negative c.d. peak at 1100 nm and low-spin ferric haem a33+-CN gives a sharp positive m.c.d. peak at 1550nm. The c.d. and m.c.d. characteristics of the 830nm absorption band in oxidized cytochrome c oxidase are not typical of type 1 blue cupric centres.

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Determination of the heme spin states in cytochrome c oxidase using magnetic circular dichroism

FEBS Letters ◽

10.1016/0014-5793(76)80877-0 ◽

1976 ◽

Vol 67 (1) ◽

pp. 94-98 ◽

Cited By ~ 16

Author(s):

A.J. Thomson ◽

T. Brittain ◽

C. Greenwood ◽

J. Springall

Keyword(s):

Circular Dichroism ◽

Cytochrome C ◽

Cytochrome C Oxidase ◽

Magnetic Circular Dichroism ◽

Spin States ◽

Circular Dichroïsm

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Spectroscopic evidence for the participation of compound A (Fea32+-O2) in the reaction of mixed-valence cytochrome c oxidase with oxygen at room temperature

Biochemical Journal ◽

10.1042/bj2150659 ◽

1983 ◽

Vol 215 (3) ◽

pp. 659-667 ◽

Cited By ~ 48

Author(s):

B C Hill ◽

C Greenwood

Keyword(s):

Electron Transfer ◽

Low Temperature ◽

Cytochrome C ◽

Cytochrome C Oxidase ◽

Valence State ◽

Room Temperature ◽

Mixed Valence ◽

Compound A ◽

Mixed Valence State ◽

Fast Phase

1. The reaction of the partially reduced mixed-valence state of cytochrome c oxidase (a3+CuA2+a3(2+)COCuB+) with O2 was studied by the rapid-reaction technique of flow-flash spectrophotometry at room temperature. Biphasic absorption records are observed in the time range up to 2 ms in both the Soret and visible spectral regions. The fast-phase rate is O2-concentration-dependent and reaches a pseudo-first-order value of 4.5 X 10(4)s-1 at 680 microM-O2 at 20 degrees C. Under the same conditions the second-phase rate is limited at 6.0 X 10(3)s-1. Kinetic difference spectra of the two species in the Soret region are not markedly different in form, whereas in the visible region two spectroscopically different species are clearly distinguished. 4. The first intermediate has a peak at 595 nm and a trough at 605 nm. The form of this spectrum resembles that seen in low-temperature studies and assigned to an O2-bound form of ferrocytochrome a3. This evidence supports a structure for oxycytochrome c oxidase with O2 bound only to cytochrome a3 and not bridged between cytochrome a3 and CuB. The second intermediate has a difference spectrum with a trough at 592 nm and a peak at 610 nm. Again, the form of this spectrum is similar to that observed during the O2 reaction at low temperature and is though to be a result of electron transfer from the oxidase to bound O2. 5. The oxygen profile of the fast phase suggests that a spectroscopically silent species may precede the formation of compound A. These data represent the first spectroscopic distinction, in the physiological temperature range, between O2 binding and electron transfer during the O2 reaction of mammalian cytochrome c oxidase. 6. A mechanism is presented for the O2 reaction of the mixed-valence state of cytochrome c oxidase involving four intermediate species. Electron transfer during this reaction is slow, relative to that seen with the fully reduced enzyme, and probably accounts for the detectability of the oxyferro species under these conditions.

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