Abstract
Flavin-containing monooxygenase (FMO) metabolizes a wide variety of nitrogen, sulfur, and phosphorous-containing xenobiotics. FMO2 is highly expressed in the lung of most mammals examined, but the protein has only recently been 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 expression, were characterized and compared with baculovirus-expressed rabbit FMO2 (rFMO2-535). Although baculovirus-expressed mFMO2-535 had properties similar 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 retained the majority of its activity. Also, mFMO2-535 was significantly less stable at elevated temperatures and in the presence of cholic acid but had greater activity in the presence of magnesium. mFMO2-535 had higher apparentKm andVmax/Km values than rFMO2-535 did in N-oxygenation assays. mFMO2-471 was correctly targeted to the membrane fraction, but N- and S-oxygenation was not detected. Since the AA sequence identity of mFMO2 and human FMO2 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, efficacy, and/or toxicity of drugs and xenobiotics for which lung is a portal of entry or target organ.
Footnotes
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Send reprint requests to: David E. Williams, Dept. of Environmental and Molecular Toxicology, and The Linus Pauling Institute, 571 Weniger, Oregon State University, Corvallis, OR 97331-6512. E-mail: david.williams{at}orst.edu
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↵1 Current Address: Department of Pharmacology, University of California San Diego, La Jolla, CA.
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↵2 Current Address: Department of Statistics, Oregon State University, Corvallis, OR.
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This work was supported in part by Grant HL38650 from The National Institutes of Health. Part of this study was presented at the 14th International Symposium on Microsomes and Drug Oxidations, Stresa, Lago Maggiore, Italy, July, 2000.
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This work was supported in part by Grant HL38650 from The National Institutes of Health. Part of this study was presented at the 14th International Symposium on Microsomes and Drug Oxidations, Stresa, Lago Maggiore, Italy, July, 2000.
- Abbreviations used are::
- FMO
- flavin-containing monooxygenase
- FMO2*1
- FMO2.1, andFMO2*2A, human alleles and proteins for full-length and truncated human FMO2, respectively
- hFMO2
- mFMO2, and rFMO2, human, monkey, and rabbit FMO isoform 2, respectively (where -471 and -535 indicate the number of AA in the truncated and full-length proteins, respectively)
- TNB
- nitro-5-thiobenzoate
- DTNB
- 5,5-dithiobis-(2-nitrobenzoate)
- CHAPS
- 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate
- DMA
- [UL-14C]-N,N′-dimethylaniline
- FAD
- flavin adenine dinucleotide
- PMSF
- phenylmethylsulfonyl fluoride
- dNTP
- 2′-deoxynucleoside-5′-triphosphate
- PCR
- polymerase chain reaction
- Sf9
- Spodoptera frugiperda
- HPLC
- high-performance liquid chromatography
- Received October 23, 2000.
- Accepted January 26, 2001.
- The American Society for Pharmacology and Experimental Therapeutics
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