Characterization of expressed full-length and truncated FMO2 from rhesus monkey

Flavin-containing monooxygenase (FMO) metabolizes a wide variety of nitroge n, sulfur, and phosphorous-containing xenobiotics. FMO2 is highly expressed in the lung of most mammals examined, but the protein has only recently be en detected in humans, presumably due to a premature stop codon at AA472 in most individuals. In this study, full-length (mFMO2-535) and 3'-truncated (mFMO2-471) monkey FMO2 protein, produced by cDNA-mediated baculovirus expr ession, were characterized and compared with baculovirus-expressed rabbit F MO2 (rFMO2-535). Although baculovirus-expressed mFMO2-535 had properties si milar to FMO in monkey lung microsomes and had catalytic properties similar to rFMO2-535, the expressed proteins differed in a number of properties in S-oxidation assays. Both enzymes had the same pH optima (pH 9.5); however, mFMO2-535 quickly lost activity at higher pH values whereas rFMO2-535 reta ined the majority of its activity. Also, mFMO2-535 was significantly less s table at elevated temperatures and in the presence of cholic acid but had g reater activity in the presence of magnesium. mFMO2-535 had higher apparent K-m and V-max/K-m values than rFMO2-535 did in N-oxygenation assays. mFMO2 -471 was correctly targeted to the membrane fraction, but N- and S-oxygenat ion was not detected. Since the AA sequence identity of mFMO2 and human FMO 2 is 97%, our results with mFMO2-535 suggest that individuals carrying the allele encoding full-length FMO2 are likely to have in vivo FMO2 activity. Such activity could result in marked differences in the metabolism, efficac y, and/or toxicity of drugs and xenobiotics for which lung is a portal of e ntry or target organ.