A novel single nucleotide polymorphism altering stability and activity of CYP2A6

CYP2A6 is known as a major cytochrome P450 (CYP) responsible for the oxidat ion of nicotine and coumarin in humans. In this study, we explored genetic polymorphisms, which reduce CYP2A6 activity in Japanese. Two novel mutation s in exon 9 of the CYP2A6 gene were found. A single nucleotide polymorphism of T1412C and G1454T resulted in Ile471Thr and Arg485Leu substitution, res pectively. The frequency of the former variant allele was considerably high (15.7%), while the latter variant appeared to be a rare polymorphism. Hete rologous expression of CYP2A6 using a cDNA possessing C instead of T-base a t codon 471 in Escherichia coli caused remarkable reduction of the stabilit y of holoenzyme at 37 degreesC. Furthermore, this variant enzyme almost lac ked nicotine C-oxidase activity, although coumarin 7-hydroxylase activity w as still observed. These data suggest that individuals homozygous for the T 1412C variant allele or heterozygous for this and a defect allele such as t he CYP2A6*4 may be poor metabolizer of nicotine, but not coumarin. (C) 2001 Academic Press.