Catalytic activities of human cytochrome P450 2C9*1, 2C9*3 and 2C9*13

Abstract

Cytochrome P450 2C9 (CYP2C9) is a geneticly polymorphic enzyme responsible for the metabolism of some clinically important drugs. CYP2C9*13 is an allele identified in a Chinese poor metabolizer of lornoxicam which has a Leu90Pro amino acid substitution. This paper reports on a study aimed at comparing the catalytic properties of CYP2C9*13 with those of the wild-type CYP2C9*1 and mutant CYP2C9*3 (Ile359Leu) in the COS-7 expression system using various substrates. CYP2C9*3 and *13 produced far lower luminescence than CYP2C9*1 in luciferin H metabolism. CYP2C9*13 exhibited an 11-fold increase in K_m but no change in V_max with tolbutamide as the substrate, a five-fold increase in K_m and an 88.8% reduction in V_max with diclofenac. These data indicate that CYP2C9*13 exhibits reduced metabolic activity toward all studied CYP2C9 substrates. The magnitude of the CYP2C9*13-associated decrease in intrinsic clearance (V_max/K_m) is greater than that associated with CYP2C9*3.

Kewords: :

• Cytochrome P450 2C9
• allelic variant
• catalytic activity

Acknowledgements

Work was supported by the National Natural Science Foundation of China, Nos. 30472062, 39930180.