Cytochrome c reduction by cysteine plus copper: a pseudosubstrate system for cytochrome c oxidase

1980 ◽  
Vol 58 (6) ◽  
pp. 499-503 ◽  
Author(s):  
Bruce C. Hill ◽  
Peter Nicholls
Keyword(s):  
Electron Transfer ◽  
Ionic Strength ◽  
Cytochrome C ◽  
Cytochrome C Oxidase ◽  
Oxygen Electrode ◽  
Horse Heart Cytochrome ◽  
Ferricytochrome C ◽  
Cytochrome C Reduction ◽  
Low Ionic Strength ◽  
Horse Heart Cytochrome C

Cysteine alone reduces horse heart cytochrome c very slowly [Formula: see text] with a rate constant virtually identical in high and low ionic strength buffers. Copper catalyzes this reaction increasing the rate by a factor of 105 in 50 mM phosphate and by a factor of 106 in 10 mM Tris buffers. When ferricytochrome c and cysteine are mixed in an oxygen electrode a "burst" of oxygen uptake is seen, the decline in which parallels the reduction of cytochrome c. When cytochrome c oxidase is added to such a mixture two routes of electron transfer to oxygen exist: enzymatic and ferricytochrome c dependent nonenzymatic. Both processes are sensitive to cyanide, but azide inhibits only the authentic cytochrome c oxidase catalyzed process and BCS the ferricytochrome c stimulated reaction.

scholarly journals Kinetics of carbon monoxide binding and electron transfer by cytochrome c polymers

1974 ◽  
Vol 141 (1) ◽  
pp. 299-304 ◽  
Author(s):  
Silvestro Dupré ◽  
Maurizio Brunori ◽  
Michael T. Wilson ◽  
Colin Greenwood
Keyword(s):  
Electron Transfer ◽  
Cytochrome C ◽  
Unique Type ◽  
Horse Heart Cytochrome ◽  
Methionine Residue ◽  
Titration Data ◽  
Carbon Monoxide Binding ◽  
Horse Heart Cytochrome C ◽  
Kinetics Of ◽  
Recombination Kinetics

Studies on horse heart cytochrome c polymers were carried out by stopped-flow and photolysis techniques, to investigate the properties of the CO complex and the kinetics of electron transfer, mainly of the dimeric and tetrameric forms. CO binding, which does not occur with native monomers, proceeds at both pH7.0 and pH9.6, and appears to follow complex kinetics: an initial phase is observed, which is CO-concentration-dependent, followed by a very slow monomolecular phase (k~2×10-3s-1 at pH7) before establishment of equilibrium. Photodissociation of the CO complex has a very low quantum yield, probably less than 0.1. Static titration data of the dimer gave an ‘n’ value of 0.4. These data strongly suggest heterogeneity of the population of binding sites, and have been interpreted in terms of the existence of different structures, probably owing to the non-unique type of binding of monomers during polymerization. Polymers of cytochrome c carboxymethylated on the methionine residue normally ligated to iron show simple CO recombination kinetics after photolytic removal (kon=1.5×106m-1·s-1 at pH6). We therefore suggest that, for native cytochrome c, polymerization has an effect on the lability of the haem crevice, rendering the iron available for binding ligands, without, however, forming the structure of a truly open crevice. Electron transfer is, on the other hand, a simple process, and no gross differences are observed between monomer and polymers. A simple model, taking into account all these data, is suggested.

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