The oxidation of ferrocytochrome c in nonbinding buffer.
Abstract: The apparent equilibrium constant and rate of oxidation was investigated for the reaction of cytochrome c with iron hexacyanide. It was found that if horse heart ferricytochrome c was exposed to ferricyanide (to oxidize traces of reduced protein) the cytochrome subsequently, even after extensive dialysis, had an apparent equilibrium constant different from that of electrodialyzed protein. The effect of ferricyanide ion apparently cannot be removed by ordinary dialysis. The ionic strength dependence of the apparent equilibrium constant and bimolecular oxidation rate constant was measured in the range 1--200 mM using Tris--cacodylate or potassium phosphate buffers at pH 7.0, and electrodialyzed horse heart cytochrome c. The oxidation reaction proceeded very rapidly. Extrapolated to zero ionic strength, kox (approximately 9 X 10(9) M-1 S-1) was about 7% of that calculated for a diffusion-limited reaction. Since the exposed heme edge occupies only the order of 3% of the surface area, electron transfer apparently results at nearly every collision with the active-site region. An effective charge of + 7.8 units was estimated for the oxidation reaction. The rate of oxidation of Pseudomonas aeruginosa c551 was much slower (kox at mu = 0 was the order of 6 X 10(3)), and was not consistent with diffusion-limited kinetics.
Publication Date: 1977-08-01 PubMed ID: 196725DOI: 10.1139/o77-118Google Scholar: Lookup
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- Journal Article
Summary
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This research studied the reaction of cytochrome c with iron hexacyanide, focusing on the apparent equilibrium constant and rate of oxidation. The study found that the reaction proceeded very rapidly and presented an effective charge of +7.8 units for the oxidation reaction.
Objective of the study
- The main objective of the study was to investigate the apparent equilibrium constant and the rate of oxidation for the reaction of cytochrome c with iron hexacyanide.
Methodology
- Researchers used horse heart ferricytochrome c exposing it to ferricyanide to oxidize traces of reduced protein.
- The ionic strength dependence of the apparent equilibrium constant and the bimolecular oxidation rate constant was measured in the range of 1–200 mM.
- The measurements were done using Tris–cacodylate or potassium phosphate buffers at pH 7.0, and electrodialyzed horse heart cytochrome c.
Key findings
- Horse heart ferricytochrome c, when exposed to ferricyanide, had an apparent equilibrium constant different from that of electrodialyzed protein.
- They found that the apparent ferricyanide ion effect cannot be removed by ordinary dialysis.
- They also concluded that the oxidation reaction proceeded very rapidly with an estimated effective charge of +7.8 units.
- Extrapolation to zero ionic strength resulted in an oxidation rate constant (kox), which was approximately 7% of the value calculated for a diffusion-limited reaction, suggesting that almost each collision with the active-site region results in electron transfer.
- The rate of oxidation of Pseudomonas aeruginosa c551 was found to be much slower and did not align with diffusion-limited kinetics.
Implications
- The results of this study highlight the rapidity of the oxidation reaction in the case of cytochrome c when in interaction with iron hexacyanide.
- It advances the understanding of the role of the ferricyanide ion in the reaction and its inability to be removed through typical dialysis.
- This research can be used as the basis for further studies on the reaction of cytochrome c with other reactants and the effect of ionic strength on said reactions.
Cite This Article
APA
Peterman BF, Morton RA.
(1977).
The oxidation of ferrocytochrome c in nonbinding buffer.
Can J Biochem, 55(8), 796-803.
https://doi.org/10.1139/o77-118 Publication
Researcher Affiliations
MeSH Terms
- Animals
- Buffers
- Computers
- Cytochrome c Group
- Dialysis
- Ferricyanides
- Horses
- Kinetics
- Mathematics
- Myocardium / enzymology
- Osmolar Concentration
- Oxidation-Reduction
Citations
This article has been cited 3 times.- Koppenol WH. Effect of a molecular dipole on the ionic strength dependence of a biomolecular rate constant. Identification of the site of reaction.. Biophys J 1980 Mar;29(3):493-507.
- Ohno N, Cusanovich MA. Reaction of C-type cytochromes with the iron hexacyanides. Mechanistic implications.. Biophys J 1981 Dec;36(3):589-605.
- Ahmad I, Cusanovich MA, Tollin G. Laser flash photolysis studies of electron transfer between semiquinone and fully reduced free flavins and horse heart cytochrome c.. Proc Natl Acad Sci U S A 1981 Nov;78(11):6724-8.
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