title: 4-Fluoro-3-nitrophenyl azide, a selective photoaffinity label for type B monoamine oxidase.
abstract: The effects of 4-fluoro-3-nitrophenyl azide (FNPA) on types A and B monoamine oxidase in rat brain cortex were studied using serotonin and phenylethylamine as substrates respectively. FNPA competitively inhibited the oxidative deamination of both serotonin (Ki = 3 microM) and phenylethylamine (Ki = 0.78 microM) in the dark. Upon photoirradiation in the presence of FNPA, a photodependent inhibition of type B MAO activity resulted. This photodependent inhibition was apparently irreversible since there was no recovery of activity upon washing of the photolyzed FNPA-enzyme mixture. Additional evidence for the photoinduced covalent binding of FNPA to type B MAO is that non-competitive inhibition kinetics resulted after photolysis. The specificity of the photodependent incorporation of FNPA to type B MAO was shown by the protective effect of phenylethylamine and by decreased [3H]pargyline labeling after the enzyme was photolyzed with FNPA. Under the same experimental conditions, only minimal photodependent inhibition of type A MAO by FNPA was found. The observed difference in the efficiencies of the photodependent inactivation of the two types of MAO by FNPA suggests that there is a conformational or a structural difference in the active sites of the two types of MAO. The active site of type B MAO could be characterized by utilizing FNPA as a photoaffinity labeling probe.
mesh_terms: D000345:Affinity Labels / Q000494:pharmacology*; D000818:Animals; D001386:Azides / Q000378:metabolism / Q000494:pharmacology*; D001665:Binding Sites; D001921:Brain / Q000201:enzymology; D007700:Kinetics; D008297:Male; D008995:Monoamine Oxidase / Q000378:metabolism*; D008996:Monoamine Oxidase Inhibitors / Q000494:pharmacology*; D010293:Pargyline / Q000378:metabolism; D010782:Photolysis; D051381:Rats; D011919:Rats, Inbred Strains; D014316:Tritium
chemical_list: D000345:Affinity Labels; D001386:Azides; D008996:Monoamine Oxidase Inhibitors; D014316:Tritium; C007753:4-fluoro-3-nitrophenyl azide; D010293:Pargyline; D008995:Monoamine Oxidase