The interconversion between monomeric and dimeric bovine heart cytochrome c oxidase

Area of Science:

• Biochemistry
• Enzyme kinetics
• Protein aggregation

Background:

• Cytochrome c oxidase (EC 1.9.3.1.) is a crucial enzyme in cellular respiration.
• Understanding its aggregation states is vital for elucidating its function.
• Previous work suggested a negative cooperative mechanism for dimeric cytochrome c oxidase.

Purpose of the Study:

• To investigate the factors influencing monomer-dimer interconversion of bovine heart cytochrome c oxidase.
• To analyze the impact of aggregation state on enzyme kinetics.
• To provide further support for the negative cooperative mechanism.

Main Methods:

• Gel filtration chromatography (Ultrogel AcA 34)
• Sucrose gradient centrifugation
• Steady-state kinetic analysis (Eadie-Hofstee plots)

Main Results:

• Monomer-dimer interconversion is modulated by ionic strength, enzyme concentration, and detergent type.
• Divalent cations and higher enzyme concentrations favor dimer formation.
• Different detergents (Triton X-100, dodecyl maltoside, Tween-80, cholate) yield distinct aggregation states.
• Enzyme kinetics differ between monomers (linear Eadie-Hofstee plots) and dimers/aggregates (nonlinear plots).

Conclusions:

• The aggregation state of cytochrome c oxidase significantly impacts its kinetic properties.
• Findings are consistent with a negative cooperative mechanism for substrate interaction with the dimeric enzyme.
• Environmental factors like ionic strength and detergent choice are critical for controlling enzyme structure and function.