Metabolism of 7-ethoxycoumarin, flavanone and steroids by cytochrome P450 2C9 variants.

CYP2C9 is a human microsomal cytochrome P450c (CYP). Much of the variation in CYP2C9 levels and activity can be attributed to polymorphisms of this gene. Wild-type CYP2C9 and mutants were coexpressed with NADPH-cytochrome P450 reductase in Escherichia coli. The hydroxylase activities toward 7-ethoxycoumarin, flavanone and steroids were examined. Six CYP2C9 variants showed Soret peaks (450 nm) typical of P450 in reduced CO-difference spectra. CYP2C9.38 had the highest 7-ethoxycoumarin de-ethylase activity. All the CYP2C9 variants showed lower flavanone 6-hydroxylation activities than CYP2C9.1 (the wild-type). CYP2C9.38 showed higher activities in testosterone 6β-hydroxylation, progesterone 6β-/16α-hydroxylation, estrone 11α-hydroxylation and estradiol 6α-hydroxylation than CYP2C9.1. CYP2C9.40 showed higher testosterone 17-oxidase activity than CYP2C9.1; CYP2C9.8 showed higher estrone 16α-hydroxylase activity and CYP2C9.12 showed higher estrone 11α-hydroxylase activity. CYP2C9.9 and CYP2C9.10 showed similar activities to CYP2C9.1. These results indicate that the substrate specificity of CYP2C9.9 and CYP2C9.10 was not changed, but CYP2C9.8, CYP2C9.12 and CYP2C9.40 showed different substrate specificity toward steroids compared with CYP2C9.1; and especially CYP2C9.38 displayed diverse substrate specificities towards 7-ethoxycoumarin and steroids.