Kinetics of electron transfer between mitochondrial cytochrome c and iron hexacyanides.

This research observes the reduction process of horse and Candida krusei cytochromes c by ferrocyanide using 1H NMR spectroscopy. The scientists discovered that electron transfer rate constants between the two are the same, but the binding association constants show a difference. This difference influences the varying reactivity between the horse and Candida cytochromes c.

Reduction of Cytochromes c by Ferrocyanide

• The study explores the reduction of two different types of cytochromes c – horse and Candida krusei – by ferrocyanide using 1H NMR spectroscopy.
• The researchers found that the reduction reaction involves a precursor complex of ferrocyanide bound to ferricytochrome c.

Electron Transfer Rate Constants & Association Constants

• Data showed that the electron transfer rate constants for the reduction of both the horse and Candida cytochromes c by associated ferrocyanide were the same, valued at 780 +/- 80 sec-1.
• Interestingly, the association constants for ferrocyanide binding to the ferricytochrome c were found to be different: 90 +/- 20 M-1 for horse and 285 +/- 30 M-1 for Candida. This indicates that the binding strength of ferrocyanide to cytochrome c is higher in the case of Candida than in horses.

Effect on Reactivity and Electron Transfer Rate for Ferrocytochrome c Oxidation

• The different association constants discerned contribute to the previously observed reactivity difference between the horse and Candida cytochromes c. This signifies that the efficiency or speed of reactions involving cytochrome c may differ depending on the species considered.
• The researchers compared the NMR data with data obtained by other kinetic methods to determine the electron transfer rate constant for the oxidation of ferrocytochrome c by associated ferricyanide. They found this value to be 4.6 +/- 1 X 10(4) sec-1.