Flavin-containing monooxygenases: mutations, disease and drug response

Phillips, Ian; Shephard, Elizabeth A.

doi:10.1016/j.tips.2008.03.004

Cited by 118 publications

(102 citation statements)

References 68 publications

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“…Mammalian FMOs (E.C.1.14.12.8) comprise a group of flavin adenine dinucleotide-containing enzymes that use NADPH and molecular oxygen to generate a 4a-hydroperoxyflavin intermediate, which mediates the twoelectron oxidation of soft, highly polarizable nucleophilic heteroatom (nitrogen, sulfur, and phosphorus)-containing xenobiotics Cashman, 1995;Cashman et al, 1995;Ziegler, 2002;Krueger and Williams, 2005;Phillips and Shephard, 2008). Our findings on the facile decomposition of compound 1 to M1 in the presence of H 2 O 2 and FMO1 are consistent with the notion that FMO1 will generally oxygenate any nucleophilic heteroatom-containing compound that can be oxidized by H 2 O 2 and/or peracids (Bruice et al, 1983).…”

Section: Discussionmentioning

confidence: 99%

Species Differences in the Oxidative Desulfurization of a Thiouracil-Based Irreversible Myeloperoxidase Inactivator by Flavin-Containing Monooxygenase Enzymes

Eng

Sharma

Wolford

et al. 2016

Drug Metabolism and Disposition

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N1-Substituted-6-arylthiouracils, represented by compound 1 [6-(2,4-dimethoxyphenyl)-1-(2-hydroxyethyl)-2-thioxo-2,3-dihydropyrimidin-4(1H)-one], are a novel class of selective irreversible inhibitors of human myeloperoxidase. The present account is a summary of our in vitro studies on the facile oxidative desulfurization in compound 1 to a cyclic ether metabolite M1 [5-(2,4-dimethoxyphenyl)-2,3-dihydro-7H-oxazolo[3,2-a]pyrimidin-7-one] in NADPH-supplemented rats (t 1/2 [half-life = mean 6 S.D.] = 8.6 6 0.4 minutes) and dog liver microsomes (t 1/2 = 11.2 6 0.4 minutes), but not in human liver microsomes (t 1/2 > 120 minutes). The in vitro metabolic instability also manifested in moderate-to-high plasma clearances of the parent compound in rats and dogs with significant concentrations of M1 detected in circulation. Mild heat deactivation of liver microsomes or coincubation with the flavin-containing monooxygenase (FMO) inhibitor imipramine significantly diminished M1 formation. In contrast, oxidative metabolism of compound 1 to M1 was not inhibited by the pan cytochrome P450 inactivator 1-aminobenzotriazole. Incubations with recombinant FMO isoforms (FMO1, FMO3, and FMO5) revealed that FMO1 principally catalyzed the conversion of compound 1 to M1. FMO1 is not expressed in adult human liver, which rationalizes the species difference in oxidative desulfurization. Oxidation by FMO1 followed Michaelis-Menten kinetics with Michaelis-Menten constant, maximum rate of oxidative desulfurization, and intrinsic clearance values of 209 mM, 20.4 nmol/min/mg protein, and 82.7 ml/min/mg protein, respectively. Addition of excess glutathione essentially eliminated the conversion of compound 1 to M1 in NADPH-supplemented rat and dog liver microsomes, which suggests that the initial FMO1-mediated S-oxygenation of compound 1 yields a sulfenic acid intermediate capable of redox cycling to the parent compound in a glutathionedependent fashion or undergoing further oxidation to a more electrophilic sulfinic acid species that is trapped intramolecularly by the pendant alcohol motif in compound 1.

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Section: Discussionmentioning

confidence: 99%

Species Differences in the Oxidative Desulfurization of a Thiouracil-Based Irreversible Myeloperoxidase Inactivator by Flavin-Containing Monooxygenase Enzymes

Eng

Sharma

Wolford

et al. 2016

Drug Metabolism and Disposition

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“…Flavin-containing monooxygenases (FMOs) 3 form a large family of enzymes present almost ubiquitously among living organisms (1,2,3). They are involved in diverse biological processes such as the biosynthesis of various natural products (4) and catabolism of xenobiotics.…”

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confidence: 99%

Joint Functions of Protein Residues and NADP(H) in Oxygen Activation by Flavin-containing Monooxygenase

Orrù

Pazmiño

Fraaije

et al. 2010

Journal of Biological Chemistry

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The reactivity of flavoenzymes with dioxygen is at the heart of a number of biochemical reactions with far reaching implications for cell physiology and pathology. Flavin-containing monooxygenases are an attractive model system to study flavin-mediated oxygenation. In these enzymes, the NADP(H) cofactor is essential for stabilizing the flavin intermediate, which activates dioxygen and makes it ready to react with the substrate undergoing oxygenation. Our studies combine site-directed mutagenesis with the usage of NADP ؉ analogues to dissect the specific roles of the cofactors and surrounding protein matrix. The highlight of this "double-engineering" approach is that subtle alterations in the hydrogen bonding and stereochemical environment can drastically alter the efficiency and outcome of the reaction with oxygen. This is illustrated by the seemingly marginal replacement of an Asn to Ser in the oxygen-reacting site, which inactivates the enzyme by effectively converting it into an oxidase. These data rationalize the effect of mutations that cause enzyme deficiency in patients affected by the fish odor syndrome. A crucial role of NADP ؉ in the oxygenation reaction is to shield the reacting flavin N5 atom by H-bond interactions. A Tyr residue functions as backdoor that stabilizes this crucial binding conformation of the nicotinamide cofactor. A general concept emerging from this analysis is that the two alternative pathways of flavoprotein-oxygen reactivity (oxidation versus monooxygenation) are predicted to have very similar activation barriers. The necessity of fine tuning the hydrogenbonding, electrostatics, and accessibility of the flavin will represent a challenge for the design and development of oxidases and monoxygenases for biotechnological applications.Flavin-containing monooxygenases (FMOs) 3 form a large family of enzymes present almost ubiquitously among living organisms (1, 2, 3). They are involved in diverse biological processes such as the biosynthesis of various natural products (4) and catabolism of xenobiotics. Humans have five different isozymes that are coded by different genes and represent a key enzymatic system in drug metabolism, whose relevance almost equals that of cytochrome P450s. Among known FMO substrates, there are metabolites directly or indirectly deriving from food digestion such as trimethylamine, drugs such as tamoxifen, and toxic molecules such as nicotine. Mutations in the gene for the isozyme 3 of human FMO (FMO3), which is most abundant in the liver, are directly responsible for trimethylaminuria, also known as fish odor syndrome (TMAU). This genetic disease causes the accumulation of trimethylamine so that the body of the patients tend to have an unpleasant smell (5, 6).Irrespectively of their biological context, FMOs always catalyze the same reaction: the oxygenation of a soft nucleophile using molecular oxygen as oxygen source and NADPH as electron donor (7) (Fig. 1A). At the heart of this very complex reaction is the stabilization of the flavin-hydroperoxide adduct res...

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“…3 A human FMO3 database has been established, 4 and causative mutations identified to date have been reported. 5,6 In addition to rare causative mutations, 15 non-synonymous single-nucleotide polymorphic (SNP) variants of FMO3 have been identified. 7 Of these, only one, p.Asn61Lys, which occurs at low frequency, results in a severe reduction of enzyme activity.…”

Section: Mutational Spectrummentioning

confidence: 99%