Cytochrome P450 2C9 (CYP2C9), a member of the CYP2C enzyme subfamily, ranks amongst the most important drug metabolizing enzymes in humans.
Human CYP2C9 has been shown to exhibit genetic polymorphism. In addition to the wild-type protein CYP2C9*1, at least 32 single nucleotide polymorphisms (SNPs) have been reported within the coding region of the CYP2C9 gene producing the variant allozymes. CYP2C9*3 is one of them. CYP2C9*3 reflects an Ile359-Leu (I359L) change in the amino acid sequence, and have reduced catalytic activity compared with the wild type (CYP2C9*1).
^Sullivan-Klose TH, Ghanayem BI, Bell DA, Zhang ZY, Kaminsky LS, Shenfield GM, Miners JO, Birkett DJ, Goldstein JA, The role of the CYP2C9-Leu359 allelic variant in the tolbutamide polymorphism， Pharmacogenetics. 1996 Aug; 6(4):341–9