The oxidation of ferrocytochrome c in nonbinding buffer.

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.