flavin-adenine-dinucleotide and hypotaurine

Out of the five isoforms of human flavin-containing monooxygenase (hFMO), FMO1 and FMO3 are the most relevant to Phase I drug metabolism. They are involved in the oxygenation of xenobiotics including drugs and pesticides using NADPH and FAD as cofactors. Majority of the characterization of these enzymes has involved hFMO3, where intermediates of its catalytic cycle have been described. On the other hand, research efforts have so far failed in capturing the same key intermediate that is responsible for the monooxygenation activity of hFMO1. In this work we demonstrate spectrophotometrically the formation of a highly stable C4a-hydroperoxyflavin intermediate of hFMO1 upon reduction by NADPH and in the presence of O

Topics: Circular Dichroism; Escherichia coli; Estrogen Antagonists; Fenthion; Flavin-Adenine Dinucleotide; Flavins; Gene Expression Regulation, Enzymologic; Humans; Insecticides; Kinetics; NADP; Oxidation-Reduction; Oxygen; Oxygenases; Tamoxifen; Taurine

The oxidation of hypotaurine to taurine, a reaction so far very poorly characterized in mammals, exhibited characteristic properties of an enzyme-catalyzed reaction in the mouse liver and brain. It was pH- and temperature-dependent and obeyed Michaelis-Menten kinetics when assayed with tissue homogenates using [35S]hypotaurine as substrate. Most of the oxidation activity was recovered in the brain in the soluble fraction whereas in the liver the activity was more evenly distributed among the subcellular fractions. The oxidation was more susceptible to heavy metals and alkylating agents in the brain than in the liver. The activity was higher in both organs in developing than in adult mice. The optimum incubation conditions for oxidation by liver homogenates included pH 9.0, oxygenation of the reaction mixture and the presence of 50 mumol/l Cu2+ and 50 mmol/l NAD+. The specificity of the enzyme(s) for hypotaurine still remains open.

Topics: Aging; Animals; Brain; Cations, Divalent; Female; Flavin-Adenine Dinucleotide; Hydrogen-Ion Concentration; Liver; Male; Mice; NAD; NADP; Oxidation-Reduction; Subcellular Fractions; Taurine; Temperature