Chen S, Shih J C, Xu Q P
Biochem Pharmacol. 1985 Mar 15;34(6):781-8. doi: 10.1016/0006-2952(85)90758-0.
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.
分别以血清素和苯乙胺为底物，研究了4-氟-3-硝基苯基叠氮化物（FNPA）对大鼠脑皮质中A、B型单胺氧化酶的影响。在黑暗中，FNPA竞争性抑制血清素（Ki = 3 microM）和苯乙胺（Ki = 0.78 microM）的氧化脱氨基作用。在FNPA存在下进行光照射时，会导致B型单胺氧化酶活性的光依赖性抑制。这种光依赖性抑制显然是不可逆的，因为在洗涤光解的FNPA-酶混合物后，活性没有恢复。FNPA与B型单胺氧化酶发生光诱导共价结合的额外证据是光解后产生非竞争性抑制动力学。苯乙胺的保护作用以及在用FNPA光解酶后[3H]帕吉林标记减少，表明了FNPA对B型单胺氧化酶光依赖性掺入的特异性。在相同的实验条件下，发现FNPA对A型单胺氧化酶只有最小程度的光依赖性抑制。观察到的FNPA对两种类型单胺氧化酶光依赖性失活效率的差异表明，两种类型单胺氧化酶的活性位点在构象或结构上存在差异。可以利用FNPA作为光亲和标记探针来表征B型单胺氧化酶的活性位点。
