Kawaji A, Ohara K, Takabatake E
Department of Toxicology, Faculty of Pharmaceutical Sciences, Setsunan University, Osaka, Japan.
Biol Pharm Bull. 1994 May;17(5):603-6. doi: 10.1248/bpb.17.603.
The activity of flavin-containing monooxygenase (FMO) in rat brain microsomes was measured by fluorometrical determination of benzydamine (BZY) N-oxygenation with HPLC. The apparent Km value for the formation of BZY N-oxide from BZY by brain microsomes was similar to that by hepatic microsomal fraction or purified FMO, but the Vmax value for brain microsomes was about one-hundredth of that for hepatic microsomes. BZY N-oxygenation activity by brain microsomes was at a maximum near pH 8.5, slightly more acidic than the optimum pH for liver FMO. BZY N-oxygenation activity was inhibited completely by heat inactivation and markedly in the presence of 1 mM thiourea, but slightly in the presence of 1 mM SKF-525A, and it was only barely activated in the presence of 5 mM n-octylamine, a positive effector of liver FMO. The addition of rabbit antisera raised against rat liver FMO resulted in 30% inhibition of BZY N-oxygenation by solubilized brain microsomes. Compared with microsomes from five different brain regions, the activity was highest in microsomes of olfactory bulbs. These results show that the activity of FMO in rat brain is distinctly determined by BZY N-oxygenation.
采用高效液相色谱荧光法测定苄达明（BZY）的N-氧化反应，以此来测定大鼠脑微粒体中含黄素单加氧酶（FMO）的活性。脑微粒体将BZY氧化生成BZY N-氧化物的表观Km值与肝微粒体组分或纯化的FMO相似，但脑微粒体的Vmax值约为肝微粒体的百分之一。脑微粒体的BZY N-氧化活性在pH 8.5附近达到最大值，比肝脏FMO的最适pH略偏酸性。BZY N-氧化活性因热失活而完全被抑制，在1 mM硫脲存在时受到显著抑制，在1 mM SKF-525A存在时受到轻微抑制，在5 mM正辛胺（肝脏FMO的一种阳性效应物）存在时仅稍有激活。添加针对大鼠肝脏FMO产生的兔抗血清可使溶解的脑微粒体的BZY N-氧化受到30%的抑制。与来自五个不同脑区的微粒体相比，嗅球微粒体中的活性最高。这些结果表明，大鼠脑中FMO的活性由BZY N-氧化明显决定。
