scholarly journals A temperature-jump study of the reaction between azurin and cytochrome c-551 from Pseudomonas aeruginosa (Short Communication)

1974 ◽  
Vol 137 (1) ◽  
pp. 113-116 ◽  
Author(s):  
Maurizio Brunori ◽  
Colin Greenwood ◽  
Michael T. Wilson
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Electron Transfer ◽  
Cytochrome C ◽  
Transfer Reaction ◽  
Short Communication ◽  
Temperature Jump ◽  
Relaxation Times ◽  
Electron Transfer Reaction ◽  
Relaxation Processes ◽  
Spectral Distributions

Temperature-jump studies on the electron-transfer reaction between azurin and cytochrome c-551 clearly reveal two chemical relaxations. The amplitudes of these relaxation processes have identical spectral distributions, but the relaxation times show different dependences on the reactant concentrations. These findings are discussed in terms of possible models.

scholarly journals Studies on partially reduced mammalian cytochrome oxidase reactions with ferrocytochrome c

1976 ◽  
Vol 157 (3) ◽  
pp. 591-598 ◽  
Author(s):  
C Greenwood ◽  
T Brittain
Keyword(s):  
Electron Transfer ◽  
Cytochrome C ◽  
Cytochrome Oxidase ◽  
Transfer Reaction ◽  
Temperature Jump ◽  
Electron Transfer Reaction ◽  
Relaxation Processes ◽  
Stopped Flow ◽  
Rapid Reduction ◽  
Ferrocytochrome C

The kinetics of the electron-transfer process which occurs between ferrocytochrome c and partially reduced mammalian cytochrome oxidase were studied by the rapid spectrophotometric techniques of stopped flow and temperature jump. Stopped-flow experiments showed initial very fast extinction changes at 605 nm and at 563 nm, indicating the simultaneous reduction of cytochrome a and oxidation of ferrocytochrome c. During this ‘burst’ phase, say the first 50 ms after mixing, it was invariably found that more cytochrome c had been oxidized than cytochrome a had been reduced. This discrepancy in electron equivalents may be accounted for by the rapid reduction of another redox site in the enzyme, possibly that associated with the extinction changes observed at 830 nm. During the incubation period in which the partially reduced oxidase was prepared, the rate of reduction of cytochrome a by ferrocytochrome c, at constant reactant concentrations, decreased with time. Temperature-jump experiments showed the presence of two relaxation processes. The faster of the two phases was assigned to the electron-transfer reaction between cytochrome c and cytochrome a. A study of the concentration-dependence of the reciprocal relaxation time for this phase yielded a rate constant of 9 X 10(6)M-1-s-1 for the electron transfer from cytochrome c to cytochrome a, and a value of 8.5 X 10(6)M-1-s-1 for the reverse reaction. The equilibrium constant for the electron-transfer reaction is therefore close to unity. The slower phase has been interpreted as signalling the transfer of electrons between cytochrome a and another redox site within the oxidase molecule.

scholarly journals Electron transfer between azurin and cytochrone c-551 from Pseudomonas aeruginosa

1975 ◽  
Vol 145 (3) ◽  
pp. 449-457 ◽  
Author(s):  
M T Wilson ◽  
C Greenwood ◽  
M Brunori ◽  
E Antonini
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Electron Transfer ◽  
Transfer Reaction ◽  
Relaxation Times ◽  
Electron Transfer Reaction ◽  
Central Feature ◽  
Cytochrome C1 ◽  
Equilibrium Data ◽  
Spectral Distributions ◽  
Rapid Reaction

The electron-transfer reaction between azurin and cytochrome c1 isolated from Pseudomonas aeruginosa was investigated by rapid-reaction techniques. Temperture-jump studies clearly reveal two chemical relaxations, the amplitudes of which have ikentical spectral distributions, but relaxation times show different dependencies on reactant concentrations. Stopped experiments also showed complex kinetics. A model is proposed which is consistent with the kinetic and equilibrium data obtained. The central feature of this model is the proposal that two intercenvertible forms of reduced azurin exist in solution, only one of which si able to participate directly in the electron-transfer reaction with cytochrome c-551. Support for the hypothesis that two forms of reduced azurin exist is derived from studies on the electron-transfer reaction between azurin and Pseudomonas cytochrome oxidase. The possible physiological significance of such a situation is discussed.

scholarly journals A temperature-jump study of the reaction between azurin and cytochrome c oxidase from Pseudomonas aeruginosa

1975 ◽  
Vol 151 (1) ◽  
pp. 185-188 ◽  
Author(s):  
M Brunori ◽  
S R Parr ◽  
C Greenwood ◽  
M T Wilson
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Electron Transfer ◽  
Cytochrome Oxidase ◽  
Cytochrome C Oxidase ◽  
Molecular Complex ◽  
Transfer Reaction ◽  
Temperature Jump ◽  
Electron Transfer Reaction ◽  
Internal Transfer ◽  
Rate Limiting

The electron-transfer reaction between azurin and the cytochrome oxidase from Pseudomonas aeruginosa was investigated by temperature-jump relaxation in the absence of O2 and in the presence of CO. The results show that: (i) reduced azurin exists in two forms in equilibrium, only one of which is capable of exchanging electrons with the Pseudomonas cytochrome oxidase, in agreement with M. T. Wilson, C. Greenwood, M. Brunori & E. Antonini (1975) (Biochem. J. 145, 449-457); (ii) the electron transfer between azurin and Pseudomonas cytochrome oxidase occurs within a molecular complex of the two proteins; this internal transfer becomes rate-limiting at high reagent concentrations.

scholarly journals The electron-transfer reaction between azurin and the cytochrome c oxidase from Pseudomonas aeruginosa

1977 ◽  
Vol 167 (2) ◽  
pp. 447-455 ◽  
Author(s):  
S R Parr ◽  
D Barber ◽  
C Greenwood ◽  
M Brunori
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Electron Transfer ◽  
Cytochrome C ◽  
Transfer Reaction ◽  
Electron Transfer Reaction ◽  
Difference Spectra ◽  
Flow Investigation ◽  
Internal Electron ◽  
Two Phases ◽  
Rate Limit

A stopped-flow investigation of the electron-transfer reaction between oxidized azurin and reduced Pseudomonas aeruginosa cytochrome c-551 oxidase and between reduced azurin and oxidized Ps. aeruginosa cytochrome c-551 oxidase was performed. Electrons leave and enter the oxidase molecule via its haem c component, with the oxidation and reduction of the haem d1 occurring by internal electron transfer. The reaction mechanism in both directions is complex. In the direction of oxidase oxidation, two phases assigned on the basis of difference spectra to haem c proceed with rate constants of 3.2 X 10(5)M-1-S-1 and 2.0 X 10(4)M-1-S-1, whereas the haem d1 oxidation occurs at 0.35 +/- 0.1S-1. Addition of CO to the reduced enzyme profoundly modifies the rate of haem c oxidation, with the faster process tending towards a rate limit of 200S-1. Reduction of the oxidase was similarly complex, with a fast haem c phase tending to a rate limit of 120S-1, and a slower phase with a second-order rate of 1.5 X 10(4)M-1-S-1; the internal transfer rate in this direction was o.25 +/- 0.1S-1. These results have been applied to a kinetic model originally developed from temperature-jump studies.

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