Six Novel Nonsynonymous CYP1A2 Gene Polymorphisms: Catalytic Activities of the Naturally Occurring Variant Enzymes

Six novel nonsynonymous nucleotide alterations were found in the cytochrome P450 1A2 gene in a Japanese population, which resulted in the following amino acid substitutions: T83M, E168Q, F186L, S212C, G299A, and T438I. These individuals were heterozygous for the amino acid substitutions. The potential functional alterations caused by the amino acid substitutions were characterized by a cDNA-mediated expression system using Chinese hamster V79 cells. Among the six CYP1A2 variants, F186L showed the most profound and statistically significant reduction in O -deethylation of phenacetin and 7-ethoxyresorufin. Kinetic analyses performed for the ethoxyresorufin O -deethylation revealed that the V max of the F186L variant was approximately 5% of that of the CYP1A2 wild type, despite a 5-fold lower K m value of the variant, the consequence of which was reduced enzymatic activity toward the substrate. Thus, for the first time, phenylalanine at residue 186 is suggested to be a critical amino acid for catalytic activity.