Further characterization of rat brain flavin-containing monooxygenase. Metabolism of imipramine to its N-oxide.
Flavin-containing monooxygenase (FMO) activity was compared in rat liver and brain microsomes by estimating the actual amount of imipramine N-oxide relative to the corresponding activity, measured using substrate-stimulated rates of NADPH oxidation. The activities measured as NADPH oxidation rates were significantly higher than those estimated from the N-oxide formed. The brain FMO activity was detectable only in the presence of detergents (sodium cholate or Lubrol PX) or in microsomes that were freeze-thawed several times. The antibody to rabbit pulmonary FMO selectively inhibited imipramine N-oxidation. The antiserum to the rat liver NADPH cytochrome P-450 reductase had no effect on imipramine N-oxidation, indicating the noninvolvement of cytochrome P-450 in the above metabolic pathway. A flavin-containing monooxygenase was partially purified from the rat brain microsomes using sequential chromatography on n-octylamino-Sepharose 4B, DEAE-Sephacel and 2',5'-ADP agarose. The purified FMO was resolved by SDS-PAGE into two bands (approximately 57 and 61 KDa, respectively) both of which cross-reacted with antibody to rabbit pulmonary FMO. The purified enzyme metabolized imipramine and the model substrate methimazole to their respective N-oxide and S-oxides.
Bhagwat
S V
SV
Department of Neurochemistry, National Institute of Mental Health and Neurosciences, Bangalore, India.
Bhamre
S
S
Boyd
M R
MR
Ravindranath
V
V
D000818:Animals; D000929:Antidepressive Agents, Tricyclic / Q000378:metabolism*; D001921:Brain / Q000201:enzymology*; D003902:Detergents / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D006863:Hydrogen-Ion Concentration; D007099:Imipramine / Q000031:analogs & derivatives* / Q000378:metabolism*; D007700:Kinetics; D008861:Microsomes / Q000201:enzymology; D008862:Microsomes, Liver / Q000201:enzymology; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction; D010105:Oxygenases / Q000302:isolation & purification / Q000378:metabolism*; D011817:Rabbits; D051381:Rats; D017208:Rats, Wistar; D012967:Sodium Dodecyl Sulfate; D013696:Temperature
D000929:Antidepressive Agents, Tricyclic; D003902:Detergents; D012967:Sodium Dodecyl Sulfate; D009249:NADP; C002921:imipramine N-oxide; D010105:Oxygenases; C020066:dimethylaniline monooxygenase (N-oxide forming); D007099:Imipramine