Flavin-containing monoxygenase

12 Flavin-Containing Monoxygenase (Cashman and Proudfoot, 1988 Kawa l et al., 1993) 

Flavin-containing monoxygenase oxidizes a variety of xenobiotics that contain nucleophilic nitrogen, sulfur, and phosphorus atoms. An early assay for this enzyme was published by Cashman and Proudfoot (1988). A more recent assay, developed by Kawaji et al. (1993) uses benzydamine, a nonsteroidal anti-inflammatory drug, as a substrate. The benzydamine N-oxide formed is fluorescent. 

Benzydamine, benzydamine N-oxide, and norbenzydamine were separated by chromatography on a LiChrosorb RP-18 column (4 mm x 150 mm). The mobile phase was methanol-acetonitrile-water-25% NH4OH [50 40 10 0.05 (v/v)]. The flow rate was 1.5 mL/min for 3 minutes, and then 3 mL/min from 3 to 20 minutes. The effluent was monitored for fluorescence using excitation and emission wavelengths of 303 and 377 nm, respectively. 

The incubation mixtures contained 0.1 M Tricine-KOH (pH 8.5), 0.5 mM NADPH, enzyme, and benzydamine in concentrations up to 1 mM (Km = 15 fiM). The final volume was 0.3 mL, and the reaction was initiated by adding benzydamine. After a 10-minute incubation at 37°C, the reaction was stopped by adding a twofold volume of methanol. The supernate obtained by centrifu- 

Microsomes were prepared from rats. The Michaelis-Menten constant of highly purified enzyme did not differ from the apparent Km of the enzyme in microsomes. Microsomes also supported formation of norbenzydamine as a result of the presence of cytochrome P450. 

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Cashman JR. Flavin-containing monoxygenase. In Ioannides C, ed. Enzyme Systems that Metabolise Drugs and Other Xenobiotics. Chichester John Wiley and Sons, 2002 67-93. 

Cashman JR, Zhang J. Human flavin-containing monoxygenases. Annu Rev Pharmacol Toxicol 2006 46 41-64. 

BURCHELL, B. and COUGHTRIE, M.W.H. (1992) UDP-glucuronosyltransferases. In Pharmacogenetics of Drug Metabolism, edited by W.Kalow, (New York Pergamon) p. 195. CASHMAN, J.R. (1995) Structural and catalytic properties of the mammalian flavin-containing monoxygenase. Chem. Res. Toxicol, 8, 165. 

Fig. 9.9 Carcinogen metabolism by human enzymes [99]. a Contributions of different (human) enzyme systems to eareinogen aetivation. b Contributions of different (human) enzyme systems to carcinogen detoxication. FMO flavin-containing monoxygenase, NAT A/-acetyl-...

Flavin Monoxygenases (FMO) These are FAD-containing enzymes that, like the CYPs, are localized in the... 

The major role of the cytochrome P450 enzymes (see Chapter 25) is to oxidize substrates and introduce oxygen to the sbucture. Similar reactions can be carried out by other flavin monoxygenases that do not contain cytochrome P450. 

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