Characterization and modulation by drugs of sheep liver microsomal flavin monooxygenase activity

Abstract

The flavin monooxygenases (FMO) catalyse the NADPH and oxygen-dependent oxidation of a wide range of nucleophilic nitrogen-, sulfur-, phosphorus-, and selenium heteroatom-containing chemicals, drugs, and agricultural agents. In the present study, sheep liver microsomal FMO activity was determined by measuring the S-oxidation rate of methimazole and the average specific activity obtained from different microsomal preparations was found to be 3.8 +/- 1.5 nmol methimazole oxidized min(-1) mg(-1) microsomal protein (mean +/- SE, n = 7). The presence of 0.1% Triton X-100 in the reaction mixture caused an increase of specific sheep liver microsomal FMO activity towards methimazole to 6.1 +/- 1.4 nmol methimazole oxidized min(-1) mg(-1) microsomal protein (mean +/- SE, n = 6). Metabolism of imipramine and chlorpromazine was measured by following the oxidation of cofactor NADPH spectrophotometrically at 340 nm. Sheep liver microsomal FMO activity towards imipramine and chlorpromazine was found to be 10.7 and 12.3 nmol NADPH oxidized min(-1) mg(-1) microsomal protein, respectively. Characterization of sheep liver enzyme was carried out using methimazole as substrate and the maximum FMO enzyme activity was detected at 37 degrees C and at pH 8.0. The apparent K(m) value of sheep liver microsomal FMO for methimazole was 0.118 mM. Effects of the detergents Triton X-100, Cholate, and Emulgen 913, on FMO activity were determined and FMO activity was found to increase with the addition of detergents to the reaction medium. Sheep liver microsomal FMO-catalysed methimazole oxidation was inhibited by imipramine and chlorpromazine when these drugs were used at high concentrations. Western blot-immunochemical analysis revealed the presence of FMO3 in sheep liver microsomes.

Phase 1 and phase 2 metabolic activities along the small intestine in adult male sheep1

“…In addition, the S ‐oxidation rate of the antithyroid drug MTZ was shown to be useful for the evaluation of FMO‐mediated metabolism in sheep liver (Longin‐Sauvageon et al. , 1998; Can Demirdöğen & Adali, 2005), as well as in camel hepatic or intestinal microsomes (Raza et al. , 2004).…”

Characterization of xenobiotic metabolizing enzymes in bovine small intestinal mucosa

“…For example, it has been shown that FMO3 is the predominant flavin‐containing isoenzyme in sheep female liver (Longin‐Sauvageon et al. , 1998), and that the S ‐oxidation rate of the antithyroid compound methimazole was useful to monitor the FMO‐mediated metabolic activity in ovine hepatic microsomes (Can Demirdöğen & Adali, 2005) and in camel hepatic or intestinal preparations (Raza et al. , 2004).…”

Benzydamine as a useful substrate of hepatic flavin‐containing monooxygenase activity in veterinary species

“…, 1998; Raza et al. , 2004; Demirdöğen & Adali, 2005). Furthermore, no comparative data are available concerning the enzymatic activity of FMO enzymes in food producing species.…”

“…, 2002; Lickteig et al ., 2009). FMOs involvement in drug metabolism was demonstrated in vitro using sheep liver microsomes (Demirdöğen & Adali, 2005; Virkel et al. , 2006), bovine liver subcellular fractions and precision‐cut slices (Santi et al.…”