Complex-formation between cytochrome c and cytochrome c peroxidase. Kinetic studies

Area of Science:

• Biochemistry
• Enzymology

Background:

• Yeast peroxidase catalyzes the oxidation of ferrocytochrome c.
• Understanding the kinetics of this reaction is crucial for elucidating enzyme mechanisms.

Purpose of the Study:

• To describe the kinetics of ferrocytochrome c peroxidation by yeast peroxidase.
• To investigate the influence of buffer composition and ionic strength on reaction rates.
• To propose a kinetic mechanism for the reaction.

Main Methods:

• Kinetic analysis of ferrocytochrome c peroxidation.
• Enzyme preparation and characterization.
• Spectrophotometric monitoring of cytochrome c oxidation.

Main Results:

• Reaction kinetics are generally first-order in phosphate buffer, but deviate in acetate buffer.
• Higher enzymic turnover and autocatalysis observed in acetate buffer.
• Formation of reversible enzyme-substrate complexes is proposed, inhibited by high ionic strength and polycations.
• Oxidized cytochrome c acts as a competitive inhibitor, with K(i) similar to K(m) for ferrocytochrome c.

Conclusions:

• The kinetics suggest a mechanism involving reversible complex formation.
• Buffer composition significantly impacts yeast peroxidase activity and reaction kinetics.
• A potential analogy exists between yeast peroxidase and mammalian cytochrome oxidase in cytochrome c oxidation.