In vitro functional analysis of human cytochrome P450 2A13 genetic variants: P450 2A13*2, *3, *4, and *10

ABSTRACTHumans possess three cytochrome P450 enzymes in the 2A subfamily (2A6, 2A7, and 2A13). P450 2A13 is mainly expressed in the human trachea and lung, whereas P450 2A6 is found in human liver. The P450 2A13 enzyme may be considered as the primary enzyme responsible for metabolic activation of many tobacco-specific carcinogens. Genetic variations significantly influence the toxicological consequences attributed to tobacco smoking. The aim of this study was to examine the in vitro functional activities of five P450 2A13 genetic variations (R257C, 133_134insT, R101Q, I331T, and R257C/I331T) in P450 2A13*2, *3, *4, and *10 alleles. Mutant clones were constructed and their recombinant enzymes were expressed in Escherichia coli. P450 2A13 mutants containing R257C, 133_134insT, I331T, and R257C/I331T displayed P450 holoenzyme spectra. The R101Q mutant was not apparently expressed. P450 2A13 enzymes displayed the typical type I binding spectra to coumarin and the calculated binding affinities of R257C, R257C...