Sites of Expression and Abundance

The gene has seven exons, and the cDNA region is 70% identical to that of the closest relative, P450 1A2. P450 1A1 is expressed in fetal liver but not at appreciable levels in adult Iiver 55 57 P45Q j i can be induced in primary human hepatocyte cultures. The dominance of P450 1A2 over 1A1 in vivo may be due to preferential induction of P450 1A2 lAl at low doses of inducers (a phenomenon established in rats ) or the presence of factors in liver that are not preserved in hepatocyte cultures. 

P450 lAl is expressed in human lung and has been partially purified . A recent estimate of a median level of P450 in human lung is 6.5 pmol/mg microsomal protein (n = 7) and 16 pmol/mg microsomal protein for smokers (n = 18) . The variation in levels of P450 lAl is very high ( 100-fold) , as suggested from earlier work in which only benzo[a]pyrene hydroxylation was used as an indicator .  

P450 lAl is also expressed in placenta and peripheral blood cells (lymphocytes, monocytes) , and these tissues have been used in many studies. Expression (at least at the mRNA level) has been reported in a number of other extrahepatic tissues including pancreas, thymus, prostate, small intestine, colon, uterus, and mammary gland .  

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