CYP2A6*6, a Novel Polymorphism in Cytochrome P450 2A6, Has a Single Amino Acid Substitution (R128Q) That Inactivates Enzymatic Activity

Abstract

By using the polymerase chain reaction technique combined with restriction enzyme fragment length polymorphism (PCR-RFLP), a novel polymorphism of CYP2A6, CYP2A6*6, was detected in 0.4% of the Japanese population. To study the enzymatic properties of the CYP2A6.6 protein with a single amino acid substitution of arginine 128 to glutamine, both this isozyme and the CYP2A6.1 protein (wild-type) were produced in insect cells using a baculovirus system. Coumarin 7-hydroxylation, which reflects CYP2A6 activity, was significantly reduced (one-eighth of normal) in cell lysate from CYP2A6*6-transfected Sf9 cells compared with that lysate from CYP2A6*1-transfected cells. To clarify the mechanism of inactivation of the CYP2A6.6 enzyme, the heme content and reduced CO difference spectrum were examined. Although CYP2A6.6 retained about onehalf the heme content of CYP2A6.1, the reduced CObound Soret peak was completely lost. These results suggest that the inactivation of CYP2A6.6 is mainly due to disordering of the holoprotein structure rather than a failure of heme incorporation.

Polymorphisms of Catechol-O-Methyltransferase in Men with Renal Cell Cancer

“…However, polymorphisms in genes have been shown to alter enzymatic activity, and in certain cases, the variant results in a reduction in activity (22). Polymorphic variants may thus play a mechanistic role by which COMT activity is reduced and result in the accumulation of mutagenic catechol compounds.…”

“…In the case of CYP2A6 and CYP2D6, the altered base causes a reduction in enzyme function (22,23). On the contrary, the variant form of the protein causes the enhanced activity of CYP1A1 and CYP1B1 enzymes (24,25).…”

Interindividual Variability in Nicotine Metabolism: C-Oxidation and Glucuronidation

“…Large interindividual variability in the cotinine formation has been demonstrated. [11][12][13][14][15] The half-lives of nicotine and cotinine after smoking are approximately 2 hr and 20 hr, respectively. 16) Because of the longer half-life of cotinine, it is generally used as a biomarker of smoking.…”

“…CYP2A6*4 allele, in which the entire CYP2A6 gene is deleted, completely lacks the enzymatic activity. [20][21][22] Alleles possessing a single nucleotide polymorphism (SNP), such as CYP2A6*2 (L160H), 23) CYP2A6*5 (G479V), 24) CYP2A6 * 6 (R128Q), 14) CYP2A6 * 7 (I471T), 25) CYP2A6*9 (T-48G in TATA box), 26) CYP2A6*10, 15,27) and CYP2A6*11 (S224P), 28) have been reported to lead to decreased enzymatic activity in vitro and W or in vivo. In our studies, the relationship between the interindividual diŠerences in nicotine metabolism to cotinine and genetic polymorphisms of the CYP2A6 gene in Japanese and Korean subjects was determined.…”

Catalog of 680 variations among eight cytochrome P450 (CYP) genes, nine esterase genes, and two other genes in the Japanese population

“…Polymorphisms of CYP2A6 that might affect enzymatic activity (Ariyoshi et al 2001;Kitagawa et al 2001;Pitarque et al 2001;Daigo et al 2002;Oscarson et al 2002;Xu et al 2002) or susceptibility to lung cancer (Pianezza et al 1998;London et al 1999;Miyamoto et al 1999) have been reported. However, some of those variants may be rare substitutions or limited to specific ethnic groups (Kitagawa et al 2001;Oscarson et al 1999Oscarson et al , 2002Xu et al 2002).…”