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Single turnover studies with oxy-cytochrome P-450cam.
Archives of Biochemistry and Biophysics
|September 1, 1986
Summary
Researchers studied the catalytic step of bacterial cytochrome P-450cam using stopped-flow spectrophotometry. The reaction kinetics revealed a hyperbolic dependence on putidaredoxin concentration, suggesting rapid binding followed by slower intracomplex steps.
Area of Science:
- Biochemistry
- Enzymology
- Chemical Kinetics
Background:
- Bacterial cytochrome P-450cam is a crucial enzyme in microbial metabolism.
- Understanding its catalytic mechanism is key to enzyme engineering and drug development.
Purpose of the Study:
- To elucidate the catalytic step of bacterial cytochrome P-450cam.
- To determine the kinetic parameters governing the reaction between cytochrome P-450cam, putidaredoxin, and oxygen.
Main Methods:
- Stopped-flow spectrophotometry was employed to monitor the reaction.
- Single-turnover reactions were initiated using reduced putidaredoxin and oxygenated camphor-bound cytochrome P-450cam.
- Metyrapone was used as an inhibitor to prevent multiple turnovers.
Main Results:
- The reaction kinetics were biphasic, with the first phase corresponding to product formation.
- Gas chromatography confirmed stoichiometric product formation.
- A hyperbolic dependence of the initial reaction rate on putidaredoxin concentration was observed (Km = 33 µM, Vmax = 53 µM/s/µM cytochrome).
Conclusions:
- The results support a kinetic model involving rapid putidaredoxin binding to cytochrome P-450cam.
- Subsequent slower intracomplex steps are proposed to occur after substrate binding.
- This study provides detailed insights into the catalytic mechanism of cytochrome P-450cam.