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Temperature-sensitive reaction intermediate of F1-ATPase
Rikiya Watanabe1, Ryota Iino, Katsuya Shimabukuro
1Department of Mechanical Engineering, University of Tokyo, Tokyo 113-8656, Japan.
EMBO Reports
|December 8, 2007
Summary
Researchers discovered a new intermediate state in F(1)-F1-ATPase molecular motor function. This state, observed at low temperatures, is identified as the enzyme
Area of Science:
- Biochemistry
- Molecular Biology
- Enzyme Kinetics
Background:
- F(1)-F1-ATPase is a rotary molecular motor essential for cellular energy production.
- Its rotation mechanism involves sequential ATP hydrolysis steps.
- Understanding intermediates is key to elucidating enzyme function.
Purpose of the Study:
- To identify and characterize novel reaction intermediates of F(1)-F1-ATPase.
- To investigate the kinetic and structural properties of these intermediates.
- To determine the role of the newly discovered intermediate in the enzyme's catalytic cycle.
Main Methods:
- Low-temperature kinetic analysis of F(1)-F1-ATPase.
- Stopped-flow spectroscopy.
- Enzyme kinetics with varying substrate and product concentrations (ATP, ADP, Pi).
Main Results:
- A new reaction intermediate was observed below 4°C, pausing at the ATP-binding angle.
- The intermediate's rate constant showed high temperature dependence (Q(10) = 19), indicating a large conformational change.
- Kinetic analyses ruled out ATP binding or hydrolysis. ADP addition prolonged the intermediate's lifetime, while inorganic phosphate shifted the pause angle, suggesting ADP release.
Conclusions:
- The newly identified intermediate represents an ADP-releasing step in the F(1)-F1-ATPase catalytic cycle.
- This finding provides new insights into the rotary mechanism and conformational dynamics of the enzyme.
- Characterization of this intermediate advances our understanding of energy transduction at the molecular level.
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