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Diffusion limited component of mitochondrial F1-ATPase
The International Journal of Biochemistry
|May 1, 1993
Summary
The rate of ATP hydrolysis by F1-ATPase is partly diffusion-controlled, as shown by viscosity experiments. Enzyme structure may also be affected by viscosity.
Area of Science:
- Biochemistry
- Enzymology
- Molecular Biophysics
Background:
- F1-ATPase is a key enzyme in cellular energy production.
- Understanding the factors limiting ATP hydrolysis rate is crucial for comprehending energy transduction.
Purpose of the Study:
- To investigate if ATP hydrolysis by F1-ATPase approaches diffusion-controlled limits.
- To determine the influence of viscosity on enzyme kinetics.
Main Methods:
- Measured catalytic rate constant (kcat) and specificity constant (kcat/Km) of F1-ATPase.
- Varied solution viscosity using viscosogenic agents.
- Tested hydrolysis of different substrates (ATP, Ca-ITP, Mg-ITP) and temperatures.
Main Results:
- kcat/Km significantly decreased with increasing viscosity.
- The decrease in kcat/Km was less pronounced for poorer substrates or lower temperatures.
- kcat was reduced by viscosity only at high concentrations of viscosogenic agents.
Conclusions:
- ATP hydrolysis by F1-ATPase is at least partially limited by the diffusion of substrates.
- Viscosity can also induce non-specific perturbations in the enzyme's structure, affecting its activity.