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Intramolecular electron transfer and binding constants in iron hexacyanide-cytochrome c complexes as studied by pulse

Y Ilan, A Shafferman

    Biochimica Et Biophysica Acta
    |October 10, 1979
    PubMed

    Insights

    Horse cytochrome c exhibits distinct internal oxidation and reduction rates when complexed with iron hexacyanide ions. Binding sites on complexes CII and CIII are kinetically similar, with moderate binding constants observed.

    Area of Science:

    • Biochemistry
    • Chemical Kinetics
    • Protein Redox Chemistry

    Background:

    • Cytochrome c is a crucial protein in cellular respiration.
    • Understanding its redox properties is vital for studying electron transfer processes.
    • Iron hexacyanide complexes serve as model redox partners.

    Purpose of the Study:

    • To determine the internal oxidation and reduction rates of horse cytochrome c.
    • To characterize the binding kinetics and affinity of iron hexacyanide ions to cytochrome c complexes.
    • To compare pulse radiolysis data with other kinetic and equilibrium techniques.

    Main Methods:

    • Pulse radiolysis was employed to measure rapid kinetic rates.
    • Spectrophotometric methods were used to determine binding constants.
    • Data were compared with Nuclear Magnetic Resonance (NMR), Temperature-jump (T-jump), and equilibrium dialysis studies.

    Main Results:

    • Internal oxidation rate of cytochrome c in complex CII was 4.6 x 10^4 s^-1.
    • Internal reduction rate of cytochrome c in complex CIII was 3.3 x 10^2 s^-1.
    • Binding sites on CII and CIII were kinetically indistinguishable with binding constants between 0.87 x 10^3 and 2 x 10^3 M^-1.

    Conclusions:

    • Horse cytochrome c displays differential redox kinetics depending on the complex.
    • Iron hexacyanide binding sites on cytochrome c complexes are highly similar kinetically.
    • Pulse radiolysis provides valuable kinetic data complementary to other biophysical methods.

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