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CYP2C9 Ile359 and Leu359 variants: enzyme kinetic study with seven substrates
K Takanashi1, H Tainaka, K Kobayashi
1Laboratory of Biochemical Pharmacology and Toxicology, Faculty of Pharmaceutical Sciences, Chiba University, Japan.
Pharmacogenetics
|April 13, 2000
Summary
The Ile359 to Leu359 substitution significantly reduces CYP2C9 enzyme activity across multiple substrates. This change impacts metabolic reaction kinetics, decreasing catalytic efficiency for various drug metabolism pathways.
Area of Science:
- Biochemistry
- Pharmacology
- Enzyme kinetics
Background:
- Cytochrome P450 2C9 (CYP2C9) is crucial for metabolizing many drugs.
- Genetic variations in CYP2C9 can alter drug efficacy and safety.
- Understanding specific amino acid substitutions is key to predicting metabolic activity.
Purpose of the Study:
- To investigate the impact of the Ile359 to Leu359 substitution on CYP2C9 enzyme activity.
- To characterize the kinetic differences between wild-type CYP2C9 and the Leu359 variant.
- To assess substrate-specific effects of this amino acid change.
Main Methods:
- Site-directed mutagenesis was used to create the CYP2C9 Leu359 variant.
- cDNA expression in yeast facilitated enzyme production.
- Detailed kinetic analysis (Vmax, Km) of seven metabolic reactions was performed.
Main Results:
- The Leu359 variant showed significantly lower Vmax/Km values (3.4- to 26.9-fold reduction) compared to wild-type CYP2C9.
- Higher Km values were observed for the Leu359 variant across all tested reactions.
- Substrate-specific variations in Vmax reduction were noted, with piroxicam hydroxylation showing the largest decrease.
Conclusions:
- The Ile359 to Leu359 substitution markedly impairs CYP2C9 catalytic activity.
- The extent of metabolic activity reduction and kinetic parameter changes are substrate-dependent.
- This substitution affects the stereoselectivity of phenytoin metabolism.