title: Contribution of N-oxygenation to the metabolism of MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) by various liver preparations.
abstract: Liver microsomes from uninduced mice and rats catalyze NADPH- and oxygen-dependent N-oxygenation of the neurotoxin MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine). The N-oxide is the principal product and accounts for 95-96% of the total MPTP metabolized by microsomes. Demethylation of MPTP is detectable but the rate of nor-MPTP formation was never more than 4-6% of the rate of N-oxygenation. Studies on the biochemical mechanisms for N-oxygenation of MPTP suggest that this reaction is catalyzed exclusively by the flavin-containing monooxygenase. This conclusion is based on the effects of selective cytochrome P-450 inhibitors, positive effectors, and alternate substrates for the flavin-containing monooxygenase as well as on studies with the purified hog liver enzyme. MPTP is an excellent substrate for this monooxygenase with a Km of 30-33 microM. Limited studies with human liver whole homogenates suggest that N-oxygenation is also a major route for the metabolism of MPTP in man and the rate of N-oxide formation is approximately equal to the rate of mitochondrial monoamine oxidase-dependent MPDP+ (1-methyl-4-phenyl-2,3-dihydropyridinium species) production.
mesh_terms: D015632:1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine; D000588:Amines / Q000494:pharmacology; D000818:Animals; D005260:Female; D005415:Flavins / Q000502:physiology; D006801:Humans; D066298:In Vitro Techniques; D008658:Inactivation, Metabolic; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008862:Microsomes, Liver / Q000378:metabolism; D010084:Oxidation-Reduction; D010105:Oxygenases / Q000502:physiology; D011725:Pyridines / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D000588:Amines; D005415:Flavins; D011725:Pyridines; D015632:1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine; D010105:Oxygenases; C008699:octylamine