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Ever-fluctuating single enzyme molecules: Michaelis-Menten equation revisited
Brian P English1, Wei Min, Antoine M van Oijen
1Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
Nature Chemical Biology
|January 18, 2006
Summary
Single enzyme molecules exhibit molecular memory, showing clustered activity at high substrate levels. The Michaelis-Menten equation remains valid, but with a new interpretation for fluctuating enzymes.
Area of Science:
- Biochemistry
- Enzymology
- Single-molecule biophysics
Background:
- Enzymes are crucial biological catalysts studied for over a century.
- The Michaelis-Menten mechanism accurately describes enzyme kinetics for large enzyme populations.
Purpose of the Study:
- To investigate the validity of the Michaelis-Menten equation at the single-molecule level.
- To explore enzyme behavior and kinetics in individual enzyme molecules.
Main Methods:
- Monitoring enzymatic turnovers of individual beta-galactosidase molecules over extended periods.
- Detecting single fluorescent product molecules released during enzymatic reactions.
Main Results:
- Observed a "molecular memory" phenomenon in single beta-galactosidase molecules at high substrate concentrations.
- Identified clusters of enzyme activity separated by periods of low activity, lasting milliseconds to seconds.
- Demonstrated that the Michaelis-Menten equation applies to fluctuating single enzymes, albeit with a revised microscopic meaning.
Conclusions:
- Enzyme dynamics at the single-molecule level reveal complex behaviors like molecular memory.
- The fundamental principles of enzyme kinetics, described by Michaelis-Menten, extend to the single-molecule realm.
- Conformational fluctuations with broad lifetime distributions underlie the observed molecular memory in enzyme activity.